28.1.22. Vector general

28.1.22.1. Assign projection

Assigns a new projection to a vector layer.

It creates a new layer with the exact same features and geometries as the input one, but assigned to a new CRS. The geometries are not reprojected, they are just assigned to a different CRS.

This algorithm can be used to repair layers which have been assigned an incorrect projection.

Attributes are not modified by this algorithm.

See also

Define Shapefile projection, Find projection, Reproject layer

Parameters

Label	Name	Type	Description
Input layer	INPUT	[vector: any]	Vector layer with wrong or missing CRS
Assigned CRS	CRS	[crs] Default: EPSG:4326 - WGS84	Select the new CRS to assign to the vector layer
Assigned CRS Optional	OUTPUT	[same as input] Default: [Create temporary layer]	Specify the output vector layer. One of: Create Temporary Layer (TEMPORARY_OUTPUT) Save to File… Save to Geopackage… Save to Database Table… Append to Layer… The file encoding can also be changed here.

Outputs

Label	Name	Type	Description
Assigned CRS	OUTPUT	[same as input]	Vector layer with assigned projection

Python code

Algorithm ID: native:assignprojection

import processing
processing.run("algorithm_id", {parameter_dictionary})

The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to run processing algorithms from the Python console.

28.1.22.2. Batch Nominatim geocoder

Performs batch geocoding using the Nominatim service against an input layer string field. The output layer will have a point geometry reflecting the geocoded location as well as a number of attributes associated to the geocoded location.

Allows features in-place modification of point features

Note

This algorithm is compliant with the usage policy of the Nominatim geocoding service provided by the OpenStreetMap Foundation.

Parameters

Label	Name	Type	Description
Input layer	INPUT	[vector: any]	Vector layer to geocode the features
Address field	FIELD	[tablefield: string]	Field containing the addresses to geocode
Geocoded	OUTPUT	[vector: point] Default: [Create temporary layer]	Specify the output layer containing only the geocoded addresses. One of: Create Temporary Layer (TEMPORARY_OUTPUT) Save to File… Save to Geopackage… Save to Database Table… Append to Layer… The file encoding can also be changed here.

Outputs

Label	Name	Type	Description
Geocoded	OUTPUT	[vector: point]	Vector layer with point features corresponding to the geocoded addresses

Python code

Algorithm ID: native:batchnominatimgeocoder

import processing
processing.run("algorithm_id", {parameter_dictionary})

The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to run processing algorithms from the Python console.

28.1.22.3. Convert layer to spatial bookmarks

Creates spatial bookmarks corresponding to the extent of features contained in a layer.

Parameters

Label	Name	Type	Description
Input Layer	INPUT	[vector: line, polygon]	The input vector layer
Bookmark destination	DESTINATION	[enumeration] Default: 0	Select the destination for the bookmarks. One of: 0 — Project bookmarks 1 — User bookmarks
Name field	NAME_EXPRESSION	[expression]	Field or expression that will give names to the generated bookmarks
Group field	GROUP_EXPRESSION	[expression]	Field or expression that will provide groups for the generated bookmarks

Outputs

Label	Name	Type	Description
Count of bookmarks added	COUNT	[number]

Python code

Algorithm ID: native:layertobookmarks

import processing
processing.run("algorithm_id", {parameter_dictionary})

The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to run processing algorithms from the Python console.

28.1.22.4. Convert spatial bookmarks to layer

Creates a new layer containing polygon features for stored spatial bookmarks. The export can be filtered to only bookmarks belonging to the current project, to all user bookmarks, or a combination of both.

Parameters

Label	Name	Type	Description
Bookmark source	SOURCE	[enumeration] [list] Default: [0,1]	Select the source(s) of the bookmarks. One or more of: 0 — Project bookmarks 1 — User bookmarks
Output CRS	CRS	[crs] Default: EPSG:4326 - WGS 84	The CRS of the output layer
Output	OUTPUT	[vector: polygon] Default: [Create temporary layer]	Specify the output layer. One of: Create Temporary Layer (TEMPORARY_OUTPUT) Save to File… Save to Geopackage… Save to Database Table… The file encoding can also be changed here.

Outputs

Label	Name	Type	Description
Output	OUTPUT	[vector: polygon]	The output (bookmarks) vector layer

Python code

Algorithm ID: native:bookmarkstolayer

import processing
processing.run("algorithm_id", {parameter_dictionary})

The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to run processing algorithms from the Python console.

28.1.22.5. Create attribute index

Creates an index against a field of the attribute table to speed up queries. The support for index creation depends on both the layer’s data provider and the field type.

No outputs are created: the index is stored on the layer itself.

Parameters

Label	Name	Type	Description
Input Layer	INPUT	[vector: any]	Select the vector layer you want to create an attribute index for
Attribute to index	FIELD	[tablefield: any]	Field of the vector layer

Outputs

Label	Name	Type	Description
Indexed layer	OUTPUT	[same as input]	A copy of the input vector layer with an index for the specified field

Python code

Algorithm ID: native:createattributeindex

import processing
processing.run("algorithm_id", {parameter_dictionary})

The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to run processing algorithms from the Python console.

28.1.22.6. Create spatial index

Creates an index to speed up access to the features in a layer based on their spatial location. Support for spatial index creation is dependent on the layer’s data provider.

No new output layers are created.

Default menu: Vector ► Data Management Tools

Parameters

Label	Name	Type	Description
Input Layer	INPUT	[vector: any]	Input vector layer

Outputs

Label	Name	Type	Description
Indexed layer	OUTPUT	[same as input]	A copy of the input vector layer with a spatial index

Python code

Algorithm ID: native:createspatialindex

import processing
processing.run("algorithm_id", {parameter_dictionary})

The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to run processing algorithms from the Python console.

28.1.22.7. Define Shapefile projection

Sets the CRS (projection) of an existing Shapefile format dataset to the provided CRS. It is very useful when a Shapefile format dataset is missing the prj file and you know the correct projection.

Contrary to the Assign projection algorithm, it modifies the current layer and will not output a new layer.

Note

For Shapefile datasets, the .prj and .qpj files will be overwritten - or created if missing - to match the provided CRS.

Default menu: Vector ► Data Management Tools

See also

Assign projection, Find projection, Reproject layer

Parameters

Label	Name	Type	Description
Input layer	INPUT	[vector: any]	Vector layer with missing projection information
CRS	CRS	[crs]	Select the CRS to assign to the vector layer

Outputs

Label	Name	Type	Description
	INPUT	[same as input]	The input vector layer with the defined projection

Python code

Algorithm ID: qgis:definecurrentprojection

import processing
processing.run("algorithm_id", {parameter_dictionary})

The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to run processing algorithms from the Python console.

28.1.22.8. Delete duplicate geometries

Finds and removes duplicated geometries.

Attributes are not checked, so in case two features have identical geometries but different attributes, only one of them will be added to the result layer.

Note

This algorithm does not require valid geometries as input.

See also

Drop geometries, Remove null geometries, Delete duplicates by attribute

Parameters

Label	Name	Type	Description
Input layer	INPUT	[vector: any]	The layer with duplicate geometries you want to clean
Cleaned	OUTPUT	[same as input] Default: [Create temporary layer]	Specify the output layer. One of: Create Temporary Layer (TEMPORARY_OUTPUT) Save to File… Save to Geopackage… Save to Database Table… The file encoding can also be changed here.

Outputs

Label	Name	Type	Description
Count of discarded duplicate records	DUPLICATE_COUNT	[number]	Count of discarded duplicate records
Cleaned	OUTPUT	[same as input]	The output layer without any duplicated geometries
Count of retained records	RETAINED_COUNT	[number]	Count of unique records

Python code

Algorithm ID: native:deleteduplicategeometries

import processing
processing.run("algorithm_id", {parameter_dictionary})

The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to run processing algorithms from the Python console.

28.1.22.9. Delete duplicates by attribute

Deletes duplicate rows by only considering the specified field / fields. The first matching row will be retained, and duplicates will be discarded.

Optionally, these duplicate records can be saved to a separate output for analysis.

See also

Delete duplicate geometries

Parameters

Label	Name	Type	Description
Input layer	INPUT	[vector: any]	The input layer
Fields to match duplicates by	FIELDS	[tablefield: any] [list]	Fields defining duplicates. Features with identical values for all these fields are considered duplicates.
Filtered (no duplicates)	OUTPUT	[same as input] Default: [Create temporary layer]	Specify the output layer containing the unique features. One of: Create Temporary Layer (TEMPORARY_OUTPUT) Save to File… Save to Geopackage… Save to Database Table… The file encoding can also be changed here.
Filtered (duplicates) Optional	DUPLICATES	[same as input] Default: [Skip output]	Specify the output layer containing only the duplicates. One of: Skip Output Create Temporary Layer (TEMPORARY_OUTPUT) Save to File… Save to Geopackage… Save to Database Table… The file encoding can also be changed here.

Outputs

Label	Name	Type	Description
Filtered (duplicates) Optional	DUPLICATES	[same as input] Default: [Skip output]	Vector layer containing the removed features. Will not be produced if not specified (left as [Skip output]).
Count of discarded duplicate records	DUPLICATE_COUNT	[number]	Count of discarded duplicate records
Filtered (no duplicates)	OUTPUT	[same as input]	Vector layer containing the unique features.
Count of retained records	RETAINED_COUNT	[number]	Count of unique records

Python code

Algorithm ID: native:removeduplicatesbyattribute

import processing
processing.run("algorithm_id", {parameter_dictionary})

The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to run processing algorithms from the Python console.

28.1.22.10. Detect dataset changes

Compares two vector layers, and determines which features are unchanged, added or deleted between the two. It is designed for comparing two different versions of the same dataset.

Fig. 28.55 Detect dataset change example

Parameters

Label	Name	Type	Description
Original layer	ORIGINAL	[vector: any]	The vector layer considered as the original version
Revised layer	REVISED	[vector: any]	The revised or modified vector layer
Attributes to consider for match Optional	COMPARE_ATTRIBUTES	[tablefield: any] [list]	Attributes to consider for match. By default, all attributes are compared.
Geometry comparison behavior Optional	MATCH_TYPE	[enumeration] Default: 1	Defines the criteria for comparison. Options: 0 — Exact Match: includes the order and vertices count of geometries 1 — Tolerant Match (Topological Equality): geometries are considered equal
Unchanged features Optional	UNCHANGED	[vector: same as Original layer]	Specify the output vector layer containing the unchanged features. One of: Skip Output Create Temporary Layer (TEMPORARY_OUTPUT) Save to File… Save to Geopackage… Save to Database Table… The file encoding can also be changed here.
Added features Optional	ADDED	[vector: same as Original layer]	Specify the output vector layer containing the added features. One of: Skip Output Create Temporary Layer (TEMPORARY_OUTPUT) Save to File… Save to Geopackage… Save to Database Table… The file encoding can also be changed here.
Deleted features Optional	DELETED	[vector: same as Original layer]	Specify the output vector layer containing the deleted features. One of: Skip Output Create Temporary Layer (TEMPORARY_OUTPUT) Save to File… Save to Geopackage… Save to Database Table… The file encoding can also be changed here.

Outputs

Label	Name	Type	Description
Unchanged features	UNCHANGED	[vector: same as Original layer]	Vector layer containing the unchanged features.
Added features	ADDED	[vector: same as Original layer]	Vector layer containing the added features.
Deleted features	DELETED	[vector: same as Original layer]	Vector layer containing the deleted features.
Count of unchanged features	UNCHANGED_COUNT	[number]	Count of unchanged features.
Count of features added in revised layer	ADDED_COUNT	[number]	Count of features added in revised layer.
Count of features deleted from original layer	DELETED_COUNT	[number]	Count of features deleted from original layer.

Python code

Algorithm ID: native:detectvectorchanges

import processing
processing.run("algorithm_id", {parameter_dictionary})

The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to run processing algorithms from the Python console.

28.1.22.11. Drop geometries

Creates a simple geometryless copy of the input layer attribute table. It keeps the attribute table of the source layer.

If the file is saved in a local folder, you can choose between many file formats.

Allows features in-place modification of point, line, and polygon features

See also

Delete duplicate geometries, Remove null geometries

Parameters

Label	Name	Type	Description
Input layer	INPUT	[vector: any]	The input vector layer
Dropped geometries	OUTPUT	[table]	Specify the output geometryless layer. One of: Create Temporary Layer (TEMPORARY_OUTPUT) Save to File… Save to Geopackage… Save to Database Table… Append to Layer… The file encoding can also be changed here.

Outputs

Label	Name	Type	Description
Dropped geometries	OUTPUT	[table]	The output geometryless layer. A copy of the original attribute table.

Python code

Algorithm ID: native:dropgeometries

import processing
processing.run("algorithm_id", {parameter_dictionary})

The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to run processing algorithms from the Python console.

28.1.22.12. Execute SQL

Runs a simple or complex query based only on SELECT with SQL syntax on the source layer.

Input datasources are identified with input1, input2… inputN and a simple query will look like SELECT * FROM input1.

Beside a simple query, you can add expressions or variables within the SQL query parameter itself. This is particulary useful if this algorithm is executed within a Processing model and you want to use a model input as a parameter of the query. An example of a query will then be SELECT * FROM [% @table %] where @table is the variable that identifies the model input.

The result of the query will be added as a new layer.

See also

SpatiaLite execute SQL, PostgreSQL execute SQL

Parameters

Label	Name	Type	Description
Additional input datasources (called input1, .., inputN in the query)	INPUT_DATASOURCES	[vector: any] [list]	List of layers to query. In the SQL editor you can refer these layers with their real name or also with input1, input2, inputN depending on how many layers have been chosen.
SQL query	INPUT_QUERY	[string]	Type the string of your SQL query, e.g. SELECT * FROM input1.
Unique identifier field Optional	INPUT_UID_FIELD	[string]	Specify the column with unique ID
Geometry field Optional	INPUT_GEOMETRY_FIELD	[string]	Specify the geometry field
Geometry type Optional	INPUT_GEOMETRY_TYPE	[enumeration] Default: 0	Choose the geometry of the result. By default the algorithm will autodetect it. One of: 0 — Autodetect 1 — No geometry 2 — Point 3 — LineString 4 — Polygon 5 — MultiPoint 6 — MultiLineString 7 — MultiPolygon
CRS Optional	INPUT_GEOMETRY_CRS	[crs]	The CRS to assign to the output layer
SQL Output	OUTPUT	[vector: any] Default: [Create temporary layer]	Specify the output layer created by the query. One of: Create Temporary Layer (TEMPORARY_OUTPUT) Save to File… Save to Geopackage… Save to Database Table… The file encoding can also be changed here.

Outputs

Label	Name	Type	Description
SQL Output	OUTPUT	[vector: any]	Vector layer created by the query

Python code

Algorithm ID: qgis:executesql

import processing
processing.run("algorithm_id", {parameter_dictionary})

The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to run processing algorithms from the Python console.

28.1.22.13. Export layers to DXF

Exports layers to DXF file. For each layer, you can choose a field whose values are used to split features in generated destination layers in DXF output.

See also

Creating new DXF files

Parameters

Label	Name	Type	Description
Input layers	LAYERS	[vector: any] [list]	List of input vector layers with options associated (filled as a QgsProcessingParameterDxfLayers item — done in GUI by pressing Configure Layer… button for each selected layer): Layer [string] (layer) Full path of the input layer to export Output layer attribute [number] (attributeIndex) Attribute index to split the input layer using unique values Output layer name [string] (overriddenLayerName) Overridden layer name to be used in the exported DXF file (the original project layer remains untouched) Allow data defined symbol blocks [boolean] (buildDataDefinedBlocks) Maximum number of symbol blocks [number] (dataDefinedBlocksMaximumNumberOfClasses) -1 means no limitation.
Symbology mode	SYMBOLOGY_MODE	[enumeration] Default: 0	Type of symbology to apply to output layers. You can choose between: 0 — No Symbology 1 — Feature Symbology 2 — Symbol Layer Symbology
Symbology scale	SYMBOLOGY_SCALE	[scale] Default: 1:1 000 000	Default scale of data export.
Map theme Optional	MAP_THEME	[map theme]	Match layer styling to the provided map theme.
Encoding	ENCODING	[enumeration]	Encoding to apply to layers.
CRS	CRS	[crs]	Choose the CRS for the output layer.
Extent Optional	EXTENT	[extent]	Limit exported features to those with geometries intersecting the provided extent.
Use layer title as name	USE_LAYER_TITLE	[boolean] Default: False	Name the output layer with the layer title (as set in layer metadata or QGIS Server properties) instead of the layer name.
Force 2D	FORCE_2D	[boolean] Default: False
Export labels as MTEXT elements	MTEXT	[boolean] Default: True	Exports labels as MTEXT or TEXT elements
Use only selected features	SELECTED_FEATURES_ONLY	[boolean] Default: False	Exports only the selected features.
DXF	OUTPUT	[file] Default: [Save to temporary file]	Specification of the output DXF file. One of: Save to a Temporary File Save to File…

Outputs

Label	Name	Type	Description
DXF	OUTPUT	[file]	.DXF file containing the input layers

Python code

Algorithm ID: native:dxfexport

import processing
processing.run("algorithm_id", {parameter_dictionary})

The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to run processing algorithms from the Python console.

28.1.22.14. Extract selected features

Saves the selected features as a new layer.

Note

If the selected layer has no selected features, the newly created layer will be empty.

Parameters

Label	Name	Type	Description
Input Layer	INPUT	[vector: any]	Layer to save the selection from
Selected features	OUTPUT	[same as input] Default: [Create temporary layer]	Specify the vector layer for the selected features. One of: Create Temporary Layer (TEMPORARY_OUTPUT) Save to File… Save to Geopackage… Save to Database Table… The file encoding can also be changed here.

Outputs

Label	Name	Type	Description
Selected features	OUTPUT	[same as input]	Vector layer with only the selected features, or no feature if none was selected.

Python code

Algorithm ID: native:saveselectedfeatures

import processing
processing.run("algorithm_id", {parameter_dictionary})

The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to run processing algorithms from the Python console.

28.1.22.15. Extract Shapefile encoding

Extracts the attribute encoding information embedded in a Shapefile. Both the encoding specified by an optional .cpg file and any encoding details present in the .dbf LDID header block are considered.

Parameters

Label	Name	Type	Description
Input Layer	INPUT	[vector: any]	ESRI Shapefile (.SHP) Layer to extract the encoding information.

Outputs

Label	Name	Type	Description
Shapefile encoding	ENCODING	[string]	Encoding information specified in the input file
CPG encoding	CPG_ENCODING	[string]	Encoding information specified in any optional .CPG file
LDID encoding	LDID_ENCODING	[string]	Encoding information specified in .dbf LDID header block

Python code

Algorithm ID: native:shpencodinginfo

import processing
processing.run("algorithm_id", {parameter_dictionary})

The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to run processing algorithms from the Python console.

28.1.22.16. Find projection

Creates a shortlist of candidate coordinate reference systems, for instance for a layer with an unknown projection.

The area that the layer is expected to cover must be specified via the target area parameter. The coordinate reference system for this target area must be known to QGIS.

The algorithm operates by testing the layer’s extent in every known reference system and then listing any for which the bounds would be near the target area if the layer was in this projection.

See also

Assign projection, Define Shapefile projection, Reproject layer

Parameters

Label	Name	Type	Description
Input Layer	INPUT	[vector: any]	Layer with unknown projection
Target area for layer (xmin, xmax, ymin, ymax)	TARGET_AREA	[extent]	The area that the layer covers. Available methods are: Calculate from layer…: uses extent of a layer loaded in the current project Calculate from layout map…: uses extent of a layout map item in the active project Calculate from bookmark…: uses extent of a saved bookmark Use map canvas extent Draw on canvas: click and drag a rectangle delimiting the area to take into account Enter the coordinates as xmin, xmax, ymin, ymax
CRS candidates	OUTPUT	[table] Default: [Create temporary layer]	Specify the table (geometryless layer) for the CRS suggestions (EPSG codes). One of: Create Temporary Layer (TEMPORARY_OUTPUT) Save to File… Save to Geopackage… Save to Database Table… The file encoding can also be changed here.

Outputs

Label	Name	Type	Description
CRS candidates	OUTPUT	[table]	A table with all the CRS (EPSG codes) of the matching criteria.

Python code

Algorithm ID: qgis:findprojection

import processing
processing.run("algorithm_id", {parameter_dictionary})

The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to run processing algorithms from the Python console.

28.1.22.17. Flatten relationship

Flattens a relationship for a vector layer, exporting a single layer containing one parent feature per related child feature. This master feature contains all the attributes for the related features. This allows to have the relation as a plain table that can be e.g. exported to CSV.

Fig. 28.56 Form of a region with related children (left) - A duplicate region feature for each related child, with joined attributes (right)

Parameters

Label	Name	Type	Description
Input Layer	INPUT	[vector: any]	Layer with the relationship that should be de-normalized
Flattened Layer Optional	OUTPUT	[same as input] Default: [Create temporary layer]	Specify the output (flattened) layer. One of: Create Temporary Layer (TEMPORARY_OUTPUT) Save to File… Save to Geopackage… Save to Database Table… The file encoding can also be changed here.

Outputs

Label	Name	Type	Description
Flattened layer	OUTPUT	[same as input]	A layer containing master features with all the attributes for the related features

Python code

Algorithm ID: native:flattenrelationships

import processing
processing.run("algorithm_id", {parameter_dictionary})

The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to run processing algorithms from the Python console.

28.1.22.18. Join attributes by field value

Takes an input vector layer and creates a new vector layer that is an extended version of the input one, with additional attributes in its attribute table.

The additional attributes and their values are taken from a second vector layer. An attribute is selected in each of them to define the join criteria.

See also

Join attributes by nearest, Join attributes by location

Parameters

Label	Name	Type	Description
Input Layer	INPUT	[vector: any]	Input vector layer. The output layer will consist of the features of this layer with attributes from matching features in the second layer.
Table field	FIELD	[tablefield: any]	Field of the source layer to use for the join
Input layer 2	INPUT_2	[vector: any]	Layer with the attribute table to join
Table field 2	FIELD_2	[tablefield: any]	Field of the second (join) layer to use for the join The type of the field must be equal to (or compatible with) the input table field type.
Layer 2 fields to copy Optional	FIELDS_TO_COPY	[tablefield: any] [list]	Select the specific fields you want to add. By default all the fields are added.
Join type	METHOD	[enumeration] Default: 1	The type of the final joined layer. One of: 0 — Create separate feature for each matching feature (one-to-many) 1 — Take attributes of the first matching feature only (one-to-one)
Discard records which could not be joined	DISCARD_NONMATCHING	[boolean] Default: True	Check if you don’t want to keep the features that could not be joined
Joined field prefix Optional	PREFIX	[string]	Add a prefix to joined fields in order to easily identify them and avoid field name collision
Joined layer Optional	OUTPUT	[same as input] Default: [Create temporary layer]	Specify the output vector layer for the join. One of: Skip Output Create Temporary Layer (TEMPORARY_OUTPUT) Save to File… Save to Geopackage… Save to Database Table… The file encoding can also be changed here.
Unjoinable features from first layer Optional	NON_MATCHING	[same as input] Default: [Skip output]	Specify the output vector layer for unjoinable features from first layer. One of: Skip Output Create Temporary Layer (TEMPORARY_OUTPUT) Save to File… Save to Geopackage… Save to Database Table… The file encoding can also be changed here.

Outputs

Label	Name	Type	Description
Number of joined features from input table	JOINED_COUNT	[number]
Unjoinable features from first layer Optional	NON_MATCHING	[same as input]	Vector layer with the non-matched features
Joined layer Optional	OUTPUT	[same as input]	Output vector layer with added attributes from the join
Number of unjoinable features from input table Optional	UNJOINABLE_COUNT	[number]

Python code

Algorithm ID: native:joinattributestable

import processing
processing.run("algorithm_id", {parameter_dictionary})

The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to run processing algorithms from the Python console.

28.1.22.19. Join attributes by location

Takes an input vector layer and creates a new vector layer that is an extended version of the input one, with additional attributes in its attribute table.

The additional attributes and their values are taken from a second vector layer. A spatial criteria is applied to select the values from the second layer that are added to each feature from the first layer.

Default menu: Vector ► Data Management Tools

See also

Join attributes by nearest, Join attributes by field value, Join attributes by location (summary)

Exploring spatial relations

Geometric predicates are boolean functions used to determine the spatial relation a feature has with another by comparing whether and how their geometries share a portion of space.

Fig. 28.57 Looking for spatial relations between layers

Using the figure above, we are looking for the green circles by spatially comparing them to the orange rectangle feature. Available geometric predicates are:

Intersect

Tests whether a geometry intersects another. Returns 1 (true) if the geometries spatially intersect (share any portion of space - overlap or touch) and 0 if they don’t. In the picture above, this will return circles 1, 2 and 3.

Contain

Returns 1 (true) if and only if no points of b lie in the exterior of a, and at least one point of the interior of b lies in the interior of a. In the picture, no circle is returned, but the rectangle would be if you would look for it the other way around, as it contains circle 1 completely. This is the opposite of are within.

Disjoint

Returns 1 (true) if the geometries do not share any portion of space (no overlap, not touching). Only circle 4 is returned.

Equal

Returns 1 (true) if and only if geometries are exactly the same. No circles will be returned.

Touch

Tests whether a geometry touches another. Returns 1 (true) if the geometries have at least one point in common, but their interiors do not intersect. Only circle 3 is returned.

Overlap

Tests whether a geometry overlaps another. Returns 1 (true) if the geometries share space, are of the same dimension, but are not completely contained by each other. Only circle 2 is returned.

Are within

Tests whether a geometry is within another. Returns 1 (true) if geometry a is completely inside geometry b. Only circle 1 is returned.

Cross

Returns 1 (true) if the supplied geometries have some, but not all, interior points in common and the actual crossing is of a lower dimension than the highest supplied geometry. For example, a line crossing a polygon will cross as a line (true). Two lines crossing will cross as a point (true). Two polygons cross as a polygon (false). In the picture, no circles will be returned.

Parameters

Label	Name	Type	Description
Join to features in	INPUT	[vector: any]	Input vector layer. The output layer will consist of the features of this layer with attributes from matching features in the second layer.
Where the features	PREDICATE	[enumeration] [list] Default: [0]	Type of spatial relation the source feature should have with the target feature so that they could be joined. One or more of: 0 — intersect 1 — contain 2 — equal 3 — touch 4 — overlap 5 — are within 6 — cross If more than one condition is chosen, at least one of them (OR operation) has to be met for a feature to be extracted.
By comparing to	JOIN	[vector: any]	The join layer. Features of this vector layer will add their attributes to the source layer attribute table if they satisfy the spatial relationship.
Fields to add (leave empty to use all fields) Optional	JOIN_FIELDS	[tablefield: any] [list]	Select the specific fields you want to add from the join layer. By default all the fields are added.
Join type	METHOD	[enumeration]	The type of the final joined layer. One of: 0 — Create separate feature for each matching feature (one-to-many) 1 — Take attributes of the first matching feature only (one-to-one) 2 — Take attributes of the feature with largest overlap only (one-to-one)
Discard records which could not be joined	DISCARD_NONMATCHING	[boolean] Default: False	Remove from the output the input layer’s features which could not be joined
Joined field prefix Optional	PREFIX	[string]	Add a prefix to joined fields in order to easily identify them and avoid field name collision
Joined layer Optional	OUTPUT	[same as input] Default: [Create temporary layer]	Specify the output vector layer for the join. One of: Skip Output Create Temporary Layer (TEMPORARY_OUTPUT) Save to File… Save to Geopackage… Save to Database Table… The file encoding can also be changed here.
Unjoinable features from first layer Optional	NON_MATCHING	[same as input] Default: [Skip output]	Specify the output vector layer for unjoinable features from first layer. One of: Skip Output Create Temporary Layer (TEMPORARY_OUTPUT) Save to File… Save to Geopackage… Save to Database Table… The file encoding can also be changed here.

Outputs

Label	Name	Type	Description
Number of joined features from input table	JOINED_COUNT	[number]
Unjoinable features from first layer Optional	NON_MATCHING	[same as input]	Vector layer of the non-matched features
Joined layer	OUTPUT	[same as input]	Output vector layer with added attributes from the join

Python code

Algorithm ID: native:joinattributesbylocation

import processing
processing.run("algorithm_id", {parameter_dictionary})

The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to run processing algorithms from the Python console.

28.1.22.20. Join attributes by location (summary)

Takes an input vector layer and creates a new vector layer that is an extended version of the input one, with additional attributes in its attribute table.

The additional attributes and their values are taken from a second vector layer. A spatial criteria is applied to select the values from the second layer that are added to each feature from the first layer.

The algorithm calculates a statistical summary for the values from matching features in the second layer (e.g. maximum value, mean value, etc).

See also

Join attributes by location

Exploring spatial relations

Geometric predicates are boolean functions used to determine the spatial relation a feature has with another by comparing whether and how their geometries share a portion of space.

Fig. 28.58 Looking for spatial relations between layers

Using the figure above, we are looking for the green circles by spatially comparing them to the orange rectangle feature. Available geometric predicates are:

Intersect

Tests whether a geometry intersects another. Returns 1 (true) if the geometries spatially intersect (share any portion of space - overlap or touch) and 0 if they don’t. In the picture above, this will return circles 1, 2 and 3.

Contain

Returns 1 (true) if and only if no points of b lie in the exterior of a, and at least one point of the interior of b lies in the interior of a. In the picture, no circle is returned, but the rectangle would be if you would look for it the other way around, as it contains circle 1 completely. This is the opposite of are within.

Disjoint

Returns 1 (true) if the geometries do not share any portion of space (no overlap, not touching). Only circle 4 is returned.

Equal

Returns 1 (true) if and only if geometries are exactly the same. No circles will be returned.

Touch

Tests whether a geometry touches another. Returns 1 (true) if the geometries have at least one point in common, but their interiors do not intersect. Only circle 3 is returned.

Overlap

Tests whether a geometry overlaps another. Returns 1 (true) if the geometries share space, are of the same dimension, but are not completely contained by each other. Only circle 2 is returned.

Are within

Tests whether a geometry is within another. Returns 1 (true) if geometry a is completely inside geometry b. Only circle 1 is returned.

Cross

Returns 1 (true) if the supplied geometries have some, but not all, interior points in common and the actual crossing is of a lower dimension than the highest supplied geometry. For example, a line crossing a polygon will cross as a line (true). Two lines crossing will cross as a point (true). Two polygons cross as a polygon (false). In the picture, no circles will be returned.

Parameters

Label	Name	Type	Description
Join to features in	INPUT	[vector: any]	Input vector layer. The output layer will consist of the features of this layer with attributes from matching features in the second layer.
Where the features	PREDICATE	[enumeration] [list] Default: [0]	Type of spatial relation the source feature should have with the target feature so that they could be joined. One or more of: 0 — intersect 1 — contain 2 — equal 3 — touch 4 — overlap 5 — are within 6 — cross If more than one condition is chosen, at least one of them (OR operation) has to be met for a feature to be extracted.
By comparing to	JOIN	[vector: any]	The join layer. Features of this vector layer will add summaries of their attributes to the source layer attribute table if they satisfy the spatial relationship.
Fields to summarize (leave empty to use all fields) Optional	JOIN_FIELDS	[tablefield: any] [list]	Select the specific fields you want to add from the join layer. By default all the fields are added.
Summaries to calculate (leave empty to use all fields) Optional	SUMMARIES	[enumeration] [list] Default: []	For each input feature, statistics are calculated on joined fields of their matching features. One or more of: 0 — count 1 — unique 2 — min 3 — max 4 — range 5 — sum 6 — mean 7 — median 8 — stddev 9 — minority 10 — majority 11 — q1 12 — q3 13 — iqr 14 — empty 15 — filled 16 — min_length 17 — max_length 18 — mean_length
Discard records which could not be joined	DISCARD_NONMATCHING	[boolean] Default: False	Remove from the output the input layer’s features which could not be joined
Joined layer	OUTPUT	[same as input] Default: [Create temporary layer]	Specify the output vector layer for the join. One of: Create Temporary Layer (TEMPORARY_OUTPUT) Save to File… Save to Geopackage… Save to Database Table… The file encoding can also be changed here.

Outputs

Label	Name	Type	Description
Joined layer	OUTPUT	[same as input]	Output vector layer with summarized attributes from the join

Python code

Algorithm ID: qgis:joinbylocationsummary

import processing
processing.run("algorithm_id", {parameter_dictionary})

The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to run processing algorithms from the Python console.

28.1.22.21. Join attributes by nearest

Takes an input vector layer and creates a new vector layer with additional fields in its attribute table. The additional attributes and their values are taken from a second vector layer. Features are joined by finding the closest features from each layer.

By default only the nearest feature is joined, but the join can also join to the k-nearest neighboring features.

If a maximum distance is specified, only features which are closer than this distance will be matched.

See also

Nearest neighbour analysis, Join attributes by field value, Join attributes by location, Distance matrix

Parameters

Label	Name	Type	Description
Input layer	INPUT	[vector: any]	The input layer.
Input layer 2	INPUT_2	[vector: any]	The join layer.
Layer 2 fields to copy (leave empty to copy all fields)	FIELDS_TO_COPY	[fields]	Join layer fields to copy (if empty, all fields will be copied).
Discard records which could not be joined	DISCARD_NONMATCHING	[boolean] Default: False	Remove from the output the input layer records which could not be joined
Joined field prefix	PREFIX	[string]	Joined field prefix
Maximum nearest neighbors	NEIGHBORS	[number] Default: 1	Maximum number of nearest neighbors
Maximum distance	MAX_DISTANCE	[number]	Maximum search distance
Joined layer Optional	OUTPUT	[same as input] Default: [Create temporary layer]	Specify the vector layer containing the joined features. One of: Skip Output Create Temporary Layer (TEMPORARY_OUTPUT) Save to File… Save to Geopackage… Save to Database Table… The file encoding can also be changed here.
Unjoinable features from first layer	NON_MATCHING	[same as input] Default: [Skip output]	Specify the vector layer containing the features that could not be joined. One of: Skip Output Create Temporary Layer (TEMPORARY_OUTPUT) Save to File… Save to Geopackage… Save to Database Table… The file encoding can also be changed here.

Outputs

Label	Name	Type	Description
Joined layer	OUTPUT	[same as input]	The output joined layer.
Unjoinable features from first layer	NON_MATCHING	[same as input]	Layer containing the features from first layer that could not be joined to any features in the join layer.
Number of joined features from input table	JOINED_COUNT	[number]	Number of features from the input table that have been joined.
Number of unjoinable features from input table	UNJOINABLE_COUNT	[number]	Number of features from the input table that could not be joined.

Python code

Algorithm ID: native:joinbynearest

import processing
processing.run("algorithm_id", {parameter_dictionary})

The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to run processing algorithms from the Python console.

28.1.22.22. Merge vector layers

Combines multiple vector layers of the same geometry type into a single one.

The attribute table of the resulting layer will contain the fields from all input layers. If fields with the same name but different types are found then the exported field will be automatically converted into a string type field. New fields storing the original layer name and source are also added.

If any input layers contain Z or M values, then the output layer will also contain these values. Similarly, if any of the input layers are multi-part, the output layer will also be a multi-part layer.

Optionally, the destination coordinate reference system (CRS) for the merged layer can be set. If it is not set, the CRS will be taken from the first input layer. All layers will be reprojected to match this CRS.

Default menu: Vector ► Data Management Tools

See also

Split vector layer

Parameters

Label	Name	Type	Description
Input Layers	LAYERS	[vector: any] [list]	The layers that are to be merged into a single layer. Layers should be of the same geometry type.
Destination CRS Optional	CRS	[crs]	Choose the CRS for the output layer. If not specified, the CRS of the first input layer is used.
Merged	OUTPUT	[same as input] Default: [Create temporary layer]	Specify the output vector layer. One of: Create Temporary Layer (TEMPORARY_OUTPUT) Save to File… Save to Geopackage… Save to Database Table… The file encoding can also be changed here.

Outputs

Label	Name	Type	Description
Merged	OUTPUT	[same as input]	Output vector layer containing all the features and attributes from the input layers.

Python code

Algorithm ID: native:mergevectorlayers

import processing
processing.run("algorithm_id", {parameter_dictionary})

The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to run processing algorithms from the Python console.

28.1.22.23. Order by expression

Sorts a vector layer according to an expression: changes the feature index according to an expression.

Be careful, it might not work as expected with some providers, the order might not be kept every time.

Parameters

Label	Name	Type	Description
Input Layer	INPUT	[vector: any]	Input vector layer to sort
Expression	EXPRESSION	[expression]	Expression to use for the sorting
Sort ascending	ASCENDING	[boolean] Default: True	If checked the vector layer will be sorted from small to large values.
Sort nulls first	NULLS_FIRST	[boolean] Default: False	If checked, Null values are placed first
Ordered	OUTPUT	[same as input] Default: [Create temporary layer]	Specify the output vector layer. One of: Create Temporary Layer (TEMPORARY_OUTPUT) Save to File… Save to Geopackage… Save to Database Table… The file encoding can also be changed here.

Outputs

Label	Name	Type	Description
Ordered	OUTPUT	[same as input]	Output (sorted) vector layer

Python code

Algorithm ID: native:orderbyexpression

import processing
processing.run("algorithm_id", {parameter_dictionary})

The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to run processing algorithms from the Python console.

28.1.22.24. Repair Shapefile

Repairs a broken ESRI Shapefile dataset by (re)creating the SHX file.

Parameters

Label	Name	Type	Description
Input Shapefile	INPUT	[file]	Full path to the ESRI Shapefile dataset with a missing or broken SHX file

Outputs

Label	Name	Type	Description
Repaired layer	OUTPUT	[vector: any]	The input vector layer with the SHX file repaired

Python code

Algorithm ID: native:repairshapefile

import processing
processing.run("algorithm_id", {parameter_dictionary})

The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to run processing algorithms from the Python console.

28.1.22.25. Reproject layer

Reprojects a vector layer in a different CRS. The reprojected layer will have the same features and attributes of the input layer.

Allows features in-place modification of point, line, and polygon features

See also

Assign projection, Define Shapefile projection, Find projection

Parameters

Basic parameters

Label	Name	Type	Description
Input Layer	INPUT	[vector: any]	Input vector layer to reproject
Target CRS	TARGET_CRS	[crs] Default: EPSG:4326 - WGS 84	Destination coordinate reference system
Convert curved geometries to straight segments	CONVERT_CURVED_GEOMETRIES	[boolean] Default: False	If checked, curved geometries will be converted to straight segments in the process, avoiding potential distortion issues.
Reprojected	OUTPUT	[same as input] Default: [Create temporary layer]	Specify the output vector layer. One of: Create Temporary Layer (TEMPORARY_OUTPUT) Save to File… Save to Geopackage… Save to Database Table… Append to Layer… The file encoding can also be changed here.

Advanced parameters

Label	Name	Type	Description
Coordinate Operation Optional	OPERATION	[string]	Specific operation to use for a particular reprojection task, instead of always forcing use of the current project’s transformation settings. Useful when reprojecting a particular layer and control over the exact transformation pipeline is required. Requires proj version >= 6. Read more at Datum Transformations.

Outputs

Label	Name	Type	Description
Reprojected	OUTPUT	[same as input]	Output (reprojected) vector layer

Python code

Algorithm ID: native:reprojectlayer

import processing
processing.run("algorithm_id", {parameter_dictionary})

The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to run processing algorithms from the Python console.

28.1.22.26. Save vector features to file

Saves vector features to a specified file dataset.

For dataset formats supporting layers, an optional layer name parameter can be used to specify a custom string. Optional GDAL-defined dataset and layer options can be specified. For more information on this, read the online GDAL documentation on the format.

Parameters

Basic parameters

Label	Name	Type	Description
Vector features	INPUT	[vector: any]	Input vector layer.
Saved features	OUTPUT	[same as input] Default: [Save to temporary file]	Specify the file to save the features to. One of: Save to a Temporary File Save to File…

Advanced parameters

Label	Name	Type	Description
Layer name Optional	LAYER_NAME	[string]	Name to use for the output layer
GDAL dataset options Optional	DATASOURCE_OPTIONS	[string]	GDAL dataset creation options of the output format. Separate individual options with semicolons.
GDAL layer options Optional	LAYER_OPTIONS	[string]	GDAL layer creation options of the output format. Separate individual options with semicolons.
Action to take on pre-existing file	ACTION_ON_EXISTING_FILE	[enumeration] Default: 0	How to manage existing features. Valid methods are: 0 — Create or overwrite file 1 — Create or overwrite layer 2 — Append features to existing layer, but do not create new fields 3 — Append features to existing layer, and create new fields if needed

Outputs

Label	Name	Type	Description
Saved features	OUTPUT	[same as input]	Vector layer with the saved features.
File name and path	FILE_PATH	[string]	Output file name and path.
Layer name	LAYER_NAME	[string]	Name of the layer, if any.

Python code

Algorithm ID: native:savefeatures

import processing
processing.run("algorithm_id", {parameter_dictionary})

The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to run processing algorithms from the Python console.

28.1.22.27. Set layer encoding

Sets the encoding used for reading a layer’s attributes. No permanent changes are made to the layer, rather it affects only how the layer is read during the current session.

Note

Changing the encoding is only supported for some vector layer data sources.

Parameters

Label	Name	Type	Description
Saved features	INPUT	[vector: any]	Vector layer to set the encoding.
Encoding	ENCODING	[string]	Text encoding to assign to the layer in the current QGIS session.

Outputs

Label	Name	Type	Description
Output layer	OUTPUT	[same as input]	Input vector layer with the set encoding.

Python code

Algorithm ID: native:setlayerencoding

import processing
processing.run("algorithm_id", {parameter_dictionary})

The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to run processing algorithms from the Python console.

28.1.22.28. Split features by character

Features are split into multiple output features by splitting a field’s value at a specified character. For instance, if a layer contains features with multiple comma separated values contained in a single field, this algorithm can be used to split these values up across multiple output features. Geometries and other attributes remain unchanged in the output. Optionally, the separator string can be a regular expression for added flexibility.

Allows features in-place modification of point, line, and polygon features

Parameters

Label	Name	Type	Description
Input Layer	INPUT	[vector: any]	Input vector layer
Split using values in the field	FIELD	[tablefield: any]	Field to use for splitting
Split value using character	CHAR	[string]	Character to use for splitting
Use regular expression separator	REGEX	[boolean] Default: False
Split	OUTPUT	[same as input] Default: Create temporary layer	Specify output vector layer. One of: Create Temporary Layer (TEMPORARY_OUTPUT) Save to File… Save to Geopackage… Save to Database Table… Append to Layer… The file encoding can also be changed here.

Outputs

Label	Name	Type	Description
Split	OUTPUT	[same as input]	The output vector layer.

Python code

Algorithm ID: native:splitfeaturesbycharacter

import processing
processing.run("algorithm_id", {parameter_dictionary})

The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to run processing algorithms from the Python console.

28.1.22.29. Split vector layer

Creates a set of vectors in an output folder based on an input layer and an attribute. The output folder will contain as many layers as the unique values found in the desired field.

The number of files generated is equal to the number of different values found for the specified attribute.

It is the opposite operation of merging.

Default menu: Vector ► Data Management Tools

See also

Merge vector layers

Parameters

Basic parameters

Label	Name	Type	Description
Input Layer	INPUT	[vector: any]	Input vector layer
Unique ID field	FIELD	[tablefield: any]	Field to use for splitting
Output directory	OUTPUT	[folder] Default: [Save to temporary folder]	Specify the directory for the output layers. One of: Save to a Temporary Directory Save to Directory

Advanced parameters

Label	Name	Type	Description
Output file type Optional	FILE_TYPE	[enumeration] Default: gpkg in the dialog window	Select the extension of the output files. If not specified or invalid, the output files format will be the one set in the “Default output vector layer extension” Processing setting.

Outputs

Label	Name	Type	Description
Output directory	OUTPUT	[folder]	The directory for the output layers
Output layers	OUTPUT_LAYERS	[same as input] [list]	The output vector layers resulting from the split.

Python code

Algorithm ID: native:splitvectorlayer

import processing
processing.run("algorithm_id", {parameter_dictionary})

The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to run processing algorithms from the Python console.

28.1.22.30. Truncate table

Truncates a layer, by deleting all features from within the layer.

Warning

This algorithm modifies the layer in place, and deleted features cannot be restored!

Parameters

Label	Name	Type	Description
Input Layer	INPUT	[vector: any]	Input vector layer

Outputs

Label	Name	Type	Description
Truncated layer	OUTPUT	[folder]	The truncated (empty) layer

Python code

Algorithm ID: native:truncatetable

import processing
processing.run("algorithm_id", {parameter_dictionary})

The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary provides the parameter NAMEs and values. See Using processing algorithms from the console for details on how to run processing algorithms from the Python console.