23.1.16. Vector overlay

23.1.16.1. Clip

Clips a vector layer using the features of an additional polygon layer.

Only the parts of the features in the input layer that fall within the polygons of the overlay layer will be added to the resulting layer.

Warning

Feature modification

The attributes of the features are not modified, although properties such as area or length of the features will be modified by the clipping operation. If such properties are stored as attributes, those attributes will have to be manually updated.

This algorithm uses spatial indexes on the providers, prepared geometries and apply a clipping operation if the geometry isn’t wholly contained by the mask geometry.

../../../../_images/clip4.png

Fig. 23.83 Clipping operation between a two-features input layer and a single feature overlay layer (left) - resulting features are moved for clarity (right)

checkbox Allows features in-place modification

Default menu: Vector ‣ Geoprocessing Tools

23.1.16.1.1. Parameters

Label

Name

Type

Description

Input layer

INPUT

[vector: any]

Layer containing the features to be clipped

Overlay layer

OVERLAY

[vector: polygon]

Layer containing the clipping features

Clipped

OUTPUT

[same as input]

Default: [Create temporary layer]

Specify the layer to contain the features from the input layer that are inside the overlay (clipping) layer. One of:

  • Create Temporary Layer

  • Save to File…

  • Save to Geopackage…

  • Save to PostGIS Table……

The file encoding can also be changed here.

23.1.16.1.2. Outputs

Label

Name

Type

Description

Clipped

OUTPUT

[same as input]

Layer containing features from the input layer split by the overlay layer.

23.1.16.1.3. Python code

Algorithm ID: qgis:clip

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.

23.1.16.2. Difference

Extracts features from the input layer that don’t fall within the boundaries of the overlay layer.

Input layer features that partially overlap the overlay layer feature(s) are split along the boundary of those feature(s) and only the portions outside the overlay layer features are retained.

Attributes are not modified (see warning).

../../../../_images/difference1.png

Fig. 23.84 Difference operation between a two-features input layer and a single feature overlay layer (left) - resulting features are moved for clarity (right)

checkbox Allows features in-place modification

Default menu: Vector ‣ Geoprocessing Tools

23.1.16.2.1. Parameters

Label

Name

Type

Description

Input layer

INPUT

[vector: any]

Layer to extract (parts of) features from.

Overlay layer

OVERLAY

[vector: any]

Layer containing the geometries that will be subtracted from the input layer geometries. It is expected to have at least as many dimensions (point: 0D, line: 1D, polygon: 2D, volume: 3D) as the input layer geometries.

Difference

OUTPUT

[same as input]

Default: [Create temporary layer]

Specify the layer to contain the (parts of) features from the input layer that are not inside the overlay layer. One of:

  • Create Temporary Layer

  • Save to File…

  • Save to Geopackage…

  • Save to PostGIS Table……

The file encoding can also be changed here.

23.1.16.2.2. Outputs

Label

Name

Type

Description

Difference

OUTPUT

[same as input]

Layer containing (parts of) features from the input layer not overlapping the overlay layer.

23.1.16.2.3. Python code

Algorithm ID: qgis:difference

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.

23.1.16.3. Extract/clip by extent

Creates a new vector layer that only contains features which fall within a specified extent.

Any features which intersect the extent will be included.

See also

Clip

23.1.16.3.1. Parameters

Label

Name

Type

Description

Input layer

INPUT

[vector: any]

Layer to extract (parts of) features from.

Extent (xmin, xmax, ymin, ymax)

EXTENT

[extent]

Extent for clipping.

Clip features to extent

CLIP

[boolean]

Default: False

If checked, output geometries will be automatically converted to multi geometries to ensure uniform output types. Moreover the geometries will be clipped to the extent chosen instead of taking the whole geometry as output.

Extracted

OUTPUT

[same as input]

Default: [Create temporary layer]

Specify the layer to contain the features from the input layer that are inside the clip extent. One of:

  • Create Temporary Layer

  • Save to File…

  • Save to Geopackage…

  • Save to PostGIS Table……

The file encoding can also be changed here.

23.1.16.3.2. Outputs

Label

Name

Type

Description

Extracted

OUTPUT

[same as input]

Layer containing the clipped features.

23.1.16.3.3. Python code

Algorithm ID: qgis:extractbyextent

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.

23.1.16.4. Intersection

Extracts the portions of features from the input layer that overlap features in the overlay layer.

Features in the intersection layer are assigned the attributes of the overlapping features from both the input and overlay layers.

Attributes are not modified (see warning).

../../../../_images/intersection.png

Fig. 23.85 The intersection operation: A two-features input layer and a single feature overlay layer (left) - resulting features are moved for clarity (right)

Default menu: Vector ‣ Geoprocessing Tools

See also

Clip, Difference

23.1.16.4.1. Parameters

Label

Name

Type

Description

Input layer

INPUT

[vector: any]

Layer to extract (parts of) features from.

Overlay layer

OVERLAY

[vector: any]

Layer containing the features to check for overlap. Its features’ geometry is expected to have at least as many dimensions (point: 0D, line: 1D, polygon: 2D, volume: 3D) as the input layer’s.

Input fields to keep (leave empty to keep all fields)

Optional

INPUT_FIELDS

[tablefield: any] [list]

Default: None

Field(s) of the input layer to keep in the output. If no fields are chosen all fields are taken.

Overlay fields to keep (leave empty to keep all fields)

Optional

OVERLAY_FIELDS

[tablefield: any] [list]

Default: None

Field(s) of the overlay layer to keep in the output. If no fields are chosen all fields are taken.

Overlay fields prefix

Optional

OVERLAY_FIELDS_PREFIX

[string]

Prefix to add to the field names of the intersect layer’s fields to avoid name collisions with fields in the input layer.

Intersection

OUTPUT

[same as input]

Default: [Create temporary layer]

Specify the layer to contain (the parts of) the features from the input layer that overlap one or more features from the overlay layer. One of:

  • Create Temporary Layer

  • Save to File…

  • Save to Geopackage…

  • Save to PostGIS Table……

The file encoding can also be changed here.

23.1.16.4.2. Outputs

Label

Name

Type

Description

Intersection

OUTPUT

[same as input]

Layer containing (parts of) features from the input layer that overlap the overlay layer.

23.1.16.4.3. Python code

Algorithm ID: qgis:intersection

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.

23.1.16.5. Line intersections

Creates point features where the lines from the two layers intersect.

../../../../_images/line_intersection.png

Fig. 23.86 Points of intersection

Default menu: Vector ‣ Analysis Tools

23.1.16.5.1. Parameters

Label

Name

Type

Description

Input layer

INPUT

[vector: line]

Input line layer.

Intersect layer

INTERSECT

[vector: line]

Layer to use to find line intersections.

Input fields to keep (leave empty to keep all fields)

Optional

INPUT_FIELDS

[tablefield: any] [list]

Default: None

Field(s) of the input layer to keep in the output. If no fields are chosen all fields are taken.

Intersect fields to keep (leave empty to keep all fields)

Optional

INTERSECT_FIELDS

[tablefield: any] [list]

Default: None

Field(s) of the intersect layer to keep in the output. If no fields are chosen all fields are taken.

Intersect fields prefix

Optional

OVERLAY_FIELDS_PREFIX

[string]

Prefix to add to the field names of the intersect layer’s fields to avoid name collisions with fields in the input layer.

Intersection

OUTPUT

[vector: point]

Default: [Create temporary layer]

Specify the layer to contain the intersection points of the lines from the input and overlay layers. One of:

  • Create Temporary Layer

  • Save to File…

  • Save to Geopackage…

  • Save to PostGIS Table……

The file encoding can also be changed here.

23.1.16.5.2. Outputs

Label

Name

Type

Description

Intersections

OUTPUT

[vector: point]

Point vector layer with the intersections.

23.1.16.5.3. Python code

Algorithm ID: qgis:lineintersections

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.

23.1.16.6. Split with lines

Splits the lines or polygons in one layer using the lines in another layer to define the breaking points. Intersection between geometries in both layers are considered as split points.

Output will contain multi geometries for split features.

../../../../_images/split_with_lines.png

Fig. 23.87 Split lines

checkbox Allows features in-place modification

23.1.16.6.1. Parameters

Label

Name

Type

Description

Input layer

INPUT

[vector: line, polygon]

Layer containing the lines or polygons to split.

Split layer

LINES

[vector: line]

Line layer whose lines are used to define the breaking points.

Split

OUTPUT

[same as input]

Default: [Create temporary layer]

Specify the layer to contain the splitted (in case they are intersected by a line in the split layer) line/polygon features from the input layer. One of:

  • Create Temporary Layer

  • Save to File…

  • Save to Geopackage…

  • Save to PostGIS Table……

The file encoding can also be changed here.

23.1.16.6.2. Outputs

Label

Name

Type

Description

Split

OUTPUT

[same as input]

Output vector layer with split lines or polygons from input layer.

23.1.16.6.3. Python code

Algorithm ID: qgis:splitwithlines

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.

23.1.16.7. Symmetrical difference

Creates a layer containing features from both the input and overlay layers but with the overlapping areas between the two layers removed.

The attribute table of the symmetrical difference layer contains attributes and fields from both the input and overlay layers.

Attributes are not modified (see warning).

../../../../_images/symmetrical_difference.png

Fig. 23.88 Symmetrical difference operation between a two-features input layer and a single feature overlay layer (left) - resulting features are moved for clarity (right)

Default menu: Vector ‣ Geoprocessing Tools

23.1.16.7.1. Parameters

Label

Name

Type

Description

Input layer

INPUT

[vector: any]

First layer to extract (parts of) features from.

Overlay layer

OVERLAY

[vector: any]

Second layer to extract (parts of) features from. Ideally the geometry type should be the same as input layer.

Overlay fields prefix

Optional

OVERLAY_FIELDS_PREFIX

[string]

Prefix to add to the field names of the overlay layer’s fields to avoid name collisions with fields in the input layer.

Symmetrical difference

OUTPUT

[same as input]

Default: [Create temporary layer]

Specify the layer to contain (the parts of) the features from the input and overlay layers that do not overlap features from the other layer. One of:

  • Create Temporary Layer

  • Save to File…

  • Save to Geopackage…

  • Save to PostGIS Table……

The file encoding can also be changed here.

23.1.16.7.2. Outputs

Label

Name

Type

Description

Symmetrical difference

OUTPUT

[same as input]

Layer containing (parts of) features from each layer not overlapping the other layer.

23.1.16.7.3. Python code

Algorithm ID: qgis:symmetricaldifference

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.

23.1.16.8. Union

Checks overlaps between features within the input layer and creates separate features for overlapping and non-overlapping parts. The area of overlap will create as many identical overlapping features as there are features that participate in that overlap.

../../../../_images/union1.png

Fig. 23.89 Union operation with a single input layer of three overlapping features (left) - resulting features are moved for clarity (right)

An overlay layer can also be used, in which case features from each layer are split at their overlap with features from the other one, creating a layer containing all the portions from both input and overlay layers. The attribute table of the union layer is filled with attribute values from the respective original layer for non-overlapping features, and attribute values from both layers for overlapping features.

../../../../_images/union_with_overlay.png

Fig. 23.90 Union operation between a two-features input layer and a single feature overlay layer (left) - resulting features are moved for clarity (right)

Note

For union(A,B) algorithm, if there are overlaps among geometries of layer A or among geometries of layer B, these are not resolved: you need to do union(union(A,B)) to resolve all overlaps, i.e. run single layer union(X) on the produced result X=union(A,B).

Default menu: Vector ‣ Geoprocessing Tools

23.1.16.8.1. Parameters

Label

Name

Type

Description

Input layer

INPUT

[vector: any]

Input vector layer to split at any intersections.

Overlay layer

Optional

OVERLAY

[vector: any]

Layer that will be combined to the first one. Ideally the geometry type should be the same as input layer.

Overlay fields prefix

Optional

OVERLAY_FIELDS_PREFIX

[string]

Prefix to add to the field names of the overlay layer’s fields to avoid name collisions with fields in the input layer.

Union

OUTPUT

[same as input]

Default: [Create temporary layer]

Specify the layer to contain the (split and duplicated) features from the input layer and the overlay layer. One of:

  • Create Temporary Layer

  • Save to File…

  • Save to Geopackage…

  • Save to PostGIS Table……

The file encoding can also be changed here.

23.1.16.8.2. Outputs

Label

Name

Type

Description

Union

OUTPUT

[same as input]

Layer containing all the overlapping and non-overlapping parts from the processed layer(s).

23.1.16.8.3. Python code

Algorithm ID: qgis:union

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.