24.1.1. Cartography

24.1.1.1. Align points to features

Calculates the rotation required to align point features with their nearest feature from another reference layer. A new field is added to the output layer which is filled with the angle (in degrees, clockwise) to the nearest reference feature.

Optionally, the output layer’s symbology can be set to automatically use the calculated rotation field to rotate marker symbols. If desired, a maximum distance to use when aligning points can be set, to avoid aligning isolated points to distant features.

Hint

This algorithm is designed for use cases like aligning building point symbols to follow the nearest road direction.

Allows features in-place modification

Parameters

Label	Name	Type	Description
Input layer	INPUT	[vector: point]	Point features to calculate the rotation for
Reference layer	REFERENCE_LAYER	[vector: any]	Layer to find the closest feature from for rotation calculation
Maximum distance to consider Optional	MAX_DISTANCE	[number] Default: Not set	If no reference feature is found within this distance, no rotation is assigned to the point feature.
Angle field name	FIELD_NAME	[string] Default: ‘rotation’	Field in which to store the rotation value.
Automatically apply symbology	APPLY_SYMBOLOGY	[boolean] Default: True	Rotates the symbol marker of the features using the angle field value
Aligned layer	OUTPUT	[vector: point] Default: [Save to temporary file]	Specify the rotated 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
Aligned layer	OUTPUT	[vector: point]	The point layer appended with a rotation field. If loaded to QGIS, it is applied by default the input layer symbology, with a data-defined rotation of its marker symbol.

Python code

Algorithm ID: native:angletonearest

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.

24.1.1.2. Combine style databases

Combines multiple QGIS style databases into a single style database. If items of the same type with the same name exist in different source databases these will be renamed to have unique names in the output combined database.

See also

Create style database from project

Parameters

Label	Name	Type	Description
Input databases	INPUT	[file] [list]	Files containing QGIS style items
Objects to combine	OBJECTS	[enumeration] [list]	Types of style items in the input databases you would like to put in the new database. These can be: 0 — Symbols 1 — Color ramps 2 — Text formats 3 — Label settings
Output style database	OUTPUT	[file] Default: [Save to temporary file]	Output .XML file combining the selected style items. One of: Save to a Temporary File Save to File…

Outputs

Label	Name	Type	Description
Color ramp count	COLORRAMPS	[number]
Label settings count	LABELSETTINGS	[number]
Output style database	OUTPUT	[file]	Output .XML file combining the selected style items
Symbol count	SYMBOLS	[number]
Text format count	TEXTFORMATS	[number]

Python code

Algorithm ID: native:combinestyles

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.

24.1.1.3. Create categorized renderer from styles

Sets a vector layer’s renderer to a categorized renderer using matching symbols from a style database. If no style file is specified, symbols from the user’s current symbol library are used instead.

A specified expression or field is used to create categories for the renderer. Each category is individually matched to the symbols which exist within the specified QGIS XML style database. Whenever a matching symbol name is found, the category’s symbol will be set to this matched symbol.

If desired, outputs can also be tables containing lists of the categories which could not be matched to symbols, and symbols which were not matched to categories.

Parameters

Label	Name	Type	Description
Input layer	INPUT	[vector: any]	Vector layer to apply a categorized style to
Categorize using expression	FIELD	[expression]	Field or expression to categorize the features
Style database (leave blank to use saved symbols)	STYLE	[file]	File (.XML) containing the symbols to apply to the input layer categories. The file can be obtained from the Style Manager Share symbols tool. If no file is specified, QGIS local symbols library is used.
Use case-sensitive match to symbol names	CASE_SENSITIVE	[boolean] Default: False	If True (checked), applies a case sensitive comparison between the categories and symbols names
Ignore non-alphanumeric characters while matching	TOLERANT	[boolean] Default: False	If True (checked), non-alphanumeric characters in the categories and symbols names will be ignored, allowing greater tolerance during the match.
Non-matching categories Optional	NON_MATCHING_CATEGORIES	[table] Default: [Skip output]	Output table for categories which do not match any symbol in the database. 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.
Non-matching symbol names Optional	NON_MATCHING_SYMBOLS	[table] Default: [Skip output]	Output table for symbols from the provided style database which do not match any category. 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
Non-matching categories	NON_MATCHING_CATEGORIES	[table]	Lists categories which could not be matched to any symbol in the provided style database
Non-matching symbol names	NON_MATCHING_SYMBOLS	[table]	Lists symbols from the provided style database which could not match any category
Categorized layer	OUTPUT	[same as input]	The input vector layer with the categorized style applied. No new layer is output.

Python code

Algorithm ID: native:categorizeusingstyle

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.

24.1.1.4. Create style database from project

Extracts all style objects (symbols, color ramps, text formats and label settings) from a QGIS project.

The extracted symbols are saved to a QGIS style database (XML format), which can be managed and imported via the Style Manager dialog.

See also

Combine style databases

Parameters

Label	Name	Type	Description
Input project (leave blank to use current) Optional	INPUT	[file]	A QGIS project file to extract the style items from
Objects to extract	OBJECTS	[enumeration] [list]	Types of style items in the input project you would like to put in the new database. These can be: 0 — Symbols 1 — Color ramps 2 — Text formats 3 — Label settings
Output style database	OUTPUT	[file] Default: [Save to temporary file]	Specify the output .XML file for the selected style items. One of: Save to a Temporary File Save to File…

Outputs

Label	Name	Type	Description
Color ramp count	COLORRAMPS	[number]	Number of color ramps
Label settings count	LABELSETTINGS	[number]	Number of label settings
Output style database	OUTPUT	[file]	Output .XML file for the selected style items
Symbol count	SYMBOLS	[number]	Number of symbols
Text format count	TEXTFORMATS	[number]	Number of text formats

Python code

Algorithm ID: native:stylefromproject

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.

24.1.1.5. Export atlas layout as image

Exports the atlas of a print layout as image files (e.g. PNG or JPEG images).

If a coverage layer is set, the selected layout’s atlas settings exposed in this algorithm will be overwritten. In this case, an empty filter or sort by expression will turn those settings off.

Parameters

Basic parameters

Label	Name	Type	Description
Atlas layout	LAYOUT	[layout]	Layout to export
Coverage layer Optional	COVERAGE_LAYER	[vector: any]	Layer to use to generate the atlas
Filter expression	FILTER_EXPRESSION	[expression]	Expression to use to filter out atlas features
Sort expression Optional	SORTBY_EXPRESSION	[expression]	Expression to use to sort the atlas features
Reverse sort order Optional	SORTBY_REVERSE	[boolean]	Determines if sorting should be inverted. Used when a sort expression is provided.
Output filename expression	FILENAME_EXPRESSION	[expression] Default: ‘output_’||@atlas_featurenumber	Expression for use to generate filenames
Output folder	FOLDER	[folder]	Destination folder where the images will be generated

Advanced parameters

Label	Name	Type	Description
Map layers to assign to unlocked map item(s) Optional	LAYERS	[enumeration] [layer]	Layers to display in the map item(s) whose contents are not locked
Image format	EXTENSION	[list] Default: png	File format of the generated output(s). The list of available formats varies depending on OS and installed drivers.
DPI Optional	DPI Default: Not set	[number]	DPI of the output file(s). If not set, the value in the print layout settings will be used.
Generate world file	GEOREFERENCE	[boolean] Default: True	Determines if a world file should be generated
Export RDF metadata	INCLUDE_METADATA	[boolean] Default: True	Determines if RDF metadata (title, author, …) should be generated
Enable antialiasing	ANTIALIAS	[boolean] Default: True	Determines if antialiasing should be enabled

Outputs

Label	Name	Type	Description
Image file	OUTPUT	[file]	Image files generated by the atlas layout

Python code

Algorithm ID: native:atlaslayouttoimage

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.

24.1.1.6. Export atlas layout as PDF

Exports the atlas of a print layout as a PDF file(s).

If a coverage layer is set, the selected layout’s atlas settings exposed in this algorithm will be overwritten. In this case, an empty filter or sort by expression will turn those settings off.

Parameters

Basic parameters

Label	Name	Type	Description
Atlas layout	LAYOUT	[layout]	Layout to export
Coverage layer Optional	COVERAGE_LAYER	[vector: any]	Layer to use to generate the atlas
Filter expression	FILTER_EXPRESSION	[expression]	Expression to use to filter out atlas features
Sort expression Optional	SORTBY_EXPRESSION	[expression]	Expression to use to sort the atlas features
Reverse sort order Optional	SORTBY_REVERSE	[boolean]	Determines if sorting should be inverted. Used when a sort expression is provided.

Advanced parameters

Label	Name	Type	Description
Map layers to assign to unlocked map item(s) Optional	LAYERS	[enumeration] [layer]	Layers to display in the map item(s) whose contents are not locked
DPI Optional	DPI Default: Not set	[number]	DPI of the output file(s). If not set, the value in the print layout settings will be used.
Always export as vectors	FORCE_VECTOR	[boolean] Default: False	Determines if vectorial data should be left as vectors
Append georeference information	GEOREFERENCE	[boolean] Default: True	Determines if a world file should be generated
Export RDF metadata	INCLUDE_METADATA	[boolean] Default: True	Determines if RDF metadata (title, author, …) should be generated
Disable tiled raster layer exports	DISABLE_TILED	[boolean] Default: False	Determines if raster should be tiled
Simplify geometries to reduce output file size	SIMPLIFY	[boolean] Default: True	Determines if geometries should be simplified to reduce output file size
Text export	TEXT_FORMAT	[list] Default: 0	Determines if text should be exported as path or text objects. Possible options are: 0 - Always export text as paths (recommended) 1 - Always export texts as text objects
PDF file	OUTPUT	[file] Default: [Save to temporary file]	Name (including path) of the output file. One of: Save to a Temporary File Save to File…

Outputs

Label	Name	Type	Description
PDF file	OUTPUT	[file]	PDF file corresponding to the exported atlas layout

Python code

Algorithm ID: native:atlaslayouttopdf

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.

24.1.1.7. Export print layout as image

Exports a print layout as an image file (e.g. PNG or JPEG images)

Parameters

Basic parameters

Label	Name	Type	Description
Print layout	LAYOUT	[layout]	Layout to export
Image file	OUTPUT	[file] Default: [Save to temporary file]	Name (including path) of the output file. One of: Save to a Temporary File Save to File…

Advanced parameters

Label	Name	Type	Description
Map layers to assign to unlocked map item(s) Optional	LAYERS	[enumeration] [layer]	Layers to display in the map item(s) whose contents are not locked
DPI Optional	DPI Default: Not set	[number]	DPI of the output file(s). If not set, the value in the print layout settings will be used.
Generate world file	GEOREFERENCE	[boolean] Default: True	Determines if a world file should be generated
Export RDF metadata	INCLUDE_METADATA	[boolean] Default: True	Determines if RDF metadata (title, author, …) should be generated
Enable antialiasing	ANTIALIAS	[boolean] Default: True	Determines if antialiasing should be enabled

Outputs

Label	Name	Type	Description
Image file	OUTPUT	[file]	Image file corresponding to the exported print layout

Python code

Algorithm ID: native:printlayouttoimage

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.

24.1.1.8. Export print layout as pdf

Exports a print layout as a PDF file.

Parameters

Basic parameters

Label	Name	Type	Description
Print Layout	LAYOUT	[layout]	Layout to export
PDF file	OUTPUT	[file] Default: [Save to temporary file]	Name (including path) of the output file. One of: Save to a Temporary File Save to File…

Advanced parameters

Label	Name	Type	Description
Map layers to assign to unlocked map item(s) Optional	LAYERS	[enumeration] [layer]	Layers to display in the map item(s) whose contents are not locked
DPI Optional	DPI Default: Not set	[number]	DPI of the output file(s). If not set, the value in the print layout settings will be used.
Always export as vectors	FORCE_VECTOR	[boolean] Default: False	Determines if vectorial data should be left as vectors
Append georeference information	GEOREFERENCE	[boolean] Default: True	Determines if a world file should be generated
Export RDF metadata	INCLUDE_METADATA	[boolean] Default: True	Determines if RDF metadata (title, author, …) should be generated
Disable tiled raster layer exports	DISABLE_TILED	[boolean] Default: False	Determines if raster should be tiled
Simplify geometries to reduce output file size	SIMPLIFY	[boolean] Default: True	Determines if geometries should be simplified to reduce output file size
Text export	TEXT_FORMAT	[list] Default: 0	Determines if text should be exported as path or text objects. Possible options are: 0 - Always export text as paths (recommended) 1 - Always export texts as text objects
Export layers as separate PDF files	SEPARATE_LAYERS	[boolean] Default: False	If True, then a separate PDF file will be created per layer per map item in the layout. Additionally, separate PDF files may be created for other complex layout items, resulting in a set of PDF files which contain logical atomic components of the layout.

Outputs

Label	Name	Type	Description
PDF file	OUTPUT	[file]	PDF file(s) corresponding to the exported print layout

Python code

Algorithm ID: native:printlayouttopdf

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.

24.1.1.9. Print layout map extent to layer

Creates a polygon layer containing the extent of a print layout map item (or items), with attributes specifying the map size (in layout units, i.e. the reference map units), scale and rotation.

If the map item parameter is specified, then only the matching map extent will be exported. If it is not specified, all map extents from the layout will be exported.

Optionally, a specific output CRS can be specified. If it is not specified, the original map item CRS will be used.

Parameters

Basic parameters

Label	Name	Type	Description
Print layout	LAYOUT	[enumeration]	A print layout in the current project
Map item Optional	MAP	[enumeration] Default: All the map items	The map item(s) whose information you want to extract. If none is provided then all the map items are processed.
Extent	OUTPUT	[vector: polygon] Default: [Create temporary layer]	Specify the output vector layer for the extent(s). 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.

Advanced parameters

Label	Name	Type	Description
Overrride CRS Optional	CRS	[crs] Default: The layout CRS	Select the CRS for the layer in which the information will be reported.

Outputs

Label	Name	Type	Description
Map height	HEIGHT	[number]
Extent	OUTPUT	[vector: polygon]	Output polygon vector layer containing extents of all the input layout map item(s)
Map rotation	ROTATION	[number]
Map scale	SCALE	[number]
Map width	WIDTH	[number]

Python code

Algorithm ID: native:printlayoutmapextenttolayer

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.

24.1.1.10. Set layer style

Applies a provided style to a layer. The style must be defined in a QML file.

No new output are created: the style is immediately assigned to the layer.

Parameters

Label	Name	Type	Description
Input Layer	INPUT	[layer]	Input layer you want to apply the style to
Style file	STYLE	[file]	Path to the .qml file of the style

Outputs

Label	Name	Type	Description
	OUTPUT	[same as input]	The input layer with the new style assigned. No new layer is created.

Python code

Algorithm ID: native:setlayerstyle

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.

24.1.1.11. Topological coloring

Assigns a color index to polygon features in such a way that no adjacent polygons share the same color index, whilst minimizing the number of colors required.

The algorithm allows choice of method to use when assigning colors.

A minimum number of colors can be specified if desired. The color index is saved to a new attribute named color_id.

The following example shows the algorithm with four different colors chosen; as you can see each color class has the same amount of features.

Fig. 24.1 Topological colors example

Parameters

Label	Name	Type	Description
Input layer	INPUT	[vector: polygon]	The input polygon layer
Minimum number of colors	MIN_COLORS	[number] Default: 4	The minimum number of colors to assign. Minimum 1, maximum 1000.
Minimum distance between features	MIN_DISTANCE	[number] Default: 0.0	Prevent nearby (but non-touching) features from being assigned equal colors. Minimum 0.0.
Balance color assignment	BALANCE	[enumeration] Default: 0	Options are: 0 — By feature count Attempts to assign colors so that the count of features assigned to each individual color index is balanced. 1 — By assigned area Assigns colors so that the total area of features assigned to each color is balanced. This mode can be useful to help avoid large features resulting in one of the colors appearing more dominant on a colored map. 2 — By distance between colors Assigns colors in order to maximize the distance between features of the same color. This mode helps to create a more uniform distribution of colors across a map.
Colored	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
Colored	OUTPUT	[vector: polygon]	Polygon vector layer with an added color_id column

Python code

Algorithm ID: qgis:topologicalcoloring

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.