Vector overlay
==============
.. only:: html
.. contents::
:local:
:depth: 1
.. _qgisclip:
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.
.. include:: ../algs_include.rst
:start-after: **warning_attributes**
:end-before: **end_warning_attributes**
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.
.. figure:: img/clip.png
:align: center
Clipping operation between a two-features input layer and a single
feature overlay layer (left) - resulting features are moved for
clarity (right)
|checkbox| Allows :ref:`features in-place modification <processing_inplace_edit>`
of point, line, and polygon features
**Default menu**: :menuselection:`Vector --> Geoprocessing Tools`
.. seealso:: :ref:`qgisintersection`, :ref:`qgisdifference`
Parameters
..........
.. list-table::
:header-rows: 1
:widths: 20 20 20 40
* - 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:
.. include:: ../algs_include.rst
:start-after: **layer_output_types**
:end-before: **end_layer_output_types**
Outputs
.......
.. list-table::
:header-rows: 1
:widths: 20 20 20 40
* - Label
- Name
- Type
- Description
* - **Clipped**
- ``OUTPUT``
- [same as input]
- Layer containing features from the input layer split by the
overlay layer.
Python code
...........
**Algorithm ID**: ``qgis:clip``
.. include:: ../algs_include.rst
:start-after: **algorithm_code_section**
:end-before: **end_algorithm_code_section**
.. _qgisdifference:
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.
.. include:: ../algs_include.rst
:start-after: **warning_attributes**
:end-before: **end_warning_attributes**
.. figure:: img/difference.png
:align: center
Difference operation between a two-features input layer and a single
feature overlay layer (left) - resulting features are moved for
clarity (right)
|checkbox| Allows :ref:`features in-place modification <processing_inplace_edit>`
of point, line, and polygon features
**Default menu**: :menuselection:`Vector --> Geoprocessing Tools`
.. seealso:: :ref:`qgissymmetricaldifference`, :ref:`qgisclip`
Parameters
..........
.. list-table::
:header-rows: 1
:widths: 20 20 20 40
* - 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:
.. include:: ../algs_include.rst
:start-after: **layer_output_types**
:end-before: **end_layer_output_types**
Outputs
.......
.. list-table::
:header-rows: 1
:widths: 20 20 20 40
* - Label
- Name
- Type
- Description
* - **Difference**
- ``OUTPUT``
- [same as input]
- Layer containing (parts of) features from the input layer
not overlapping the overlay layer.
Python code
...........
**Algorithm ID**: ``qgis:difference``
.. include:: ../algs_include.rst
:start-after: **algorithm_code_section**
:end-before: **end_algorithm_code_section**
.. _qgisextractbyextent:
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.
.. figure:: img/extractbyextent.png
:align: center
Extract operation between a three-feature input layer 'a' and a dashed extent (left) -
resulting features with dashed extent for reference (right)
.. seealso:: :ref:`qgisclip`
Parameters
..........
.. list-table::
:header-rows: 1
:widths: 20 20 20 40
* - 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.
.. include:: ../algs_include.rst
:start-after: **extent_options**
:end-before: **end_extent_options**
* - **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.
.. figure:: img/extractbyextent_clip.png
:align: center
Extract operation between a three-feature input layer 'a' and a dashed extent (left) -
resulting features with dashed extent for reference (right)
* - **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:
.. include:: ../algs_include.rst
:start-after: **layer_output_types**
:end-before: **end_layer_output_types**
Outputs
.......
.. list-table::
:header-rows: 1
:widths: 20 20 20 40
* - Label
- Name
- Type
- Description
* - **Extracted**
- ``OUTPUT``
- [same as input]
- Layer containing the clipped features.
Python code
...........
**Algorithm ID**: ``qgis:extractbyextent``
.. include:: ../algs_include.rst
:start-after: **algorithm_code_section**
:end-before: **end_algorithm_code_section**
.. _qgisintersection:
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.
.. include:: ../algs_include.rst
:start-after: **warning_attributes**
:end-before: **end_warning_attributes**
.. figure:: img/intersection.png
:align: center
The intersection operation: A two-features input layer and a single
feature overlay layer (left) - resulting features are moved for
clarity (right)
**Default menu**: :menuselection:`Vector --> Geoprocessing Tools`
.. seealso:: :ref:`qgisclip`, :ref:`qgisdifference`
Parameters
..........
.. list-table::
:header-rows: 1
:widths: 20 20 20 40
:class: longtable
* - 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:
.. include:: ../algs_include.rst
:start-after: **layer_output_types**
:end-before: **end_layer_output_types**
Outputs
.......
.. list-table::
:header-rows: 1
:widths: 20 20 20 40
:class: longtable
* - Label
- Name
- Type
- Description
* - **Intersection**
- ``OUTPUT``
- [same as input]
- Layer containing (parts of) features from the input
layer that overlap the overlay layer.
Python code
...........
**Algorithm ID**: ``qgis:intersection``
.. include:: ../algs_include.rst
:start-after: **algorithm_code_section**
:end-before: **end_algorithm_code_section**
.. _qgislineintersections:
Line intersections
------------------
Creates point features where the lines from the two layers intersect.
.. figure:: img/line_intersection.png
:align: center
Points of intersection
**Default menu**: :menuselection:`Vector --> Analysis Tools`
Parameters
..........
Basic parameters
^^^^^^^^^^^^^^^^
.. list-table::
:header-rows: 1
:widths: 20 20 20 40
:class: longtable
* - 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.
* - **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:
.. include:: ../algs_include.rst
:start-after: **layer_output_types**
:end-before: **end_layer_output_types**
Advanced parameters
^^^^^^^^^^^^^^^^^^^^
.. list-table::
:header-rows: 1
:widths: 20 20 20 40
:class: longtable
* - Label
- Name
- Type
- Description
* - **Intersect fields prefix**
Optional
- ``INTERSECT_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.
Outputs
.......
.. list-table::
:header-rows: 1
:widths: 20 20 20 40
* - Label
- Name
- Type
- Description
* - **Intersections**
- ``OUTPUT``
- [vector: point]
- Point vector layer with the intersections.
Python code
...........
**Algorithm ID**: ``qgis:lineintersections``
.. include:: ../algs_include.rst
:start-after: **algorithm_code_section**
:end-before: **end_algorithm_code_section**
.. _qgissplitwithlines:
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.
.. figure:: img/split_with_lines.png
:align: center
Split lines
|checkbox| Allows :ref:`features in-place modification <processing_inplace_edit>`
of line and polygon features
Parameters
..........
.. list-table::
:header-rows: 1
:widths: 20 20 20 40
* - 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:
.. include:: ../algs_include.rst
:start-after: **layer_output_types**
:end-before: **end_layer_output_types**
Outputs
.......
.. list-table::
:header-rows: 1
:widths: 20 20 20 40
* - Label
- Name
- Type
- Description
* - **Split**
- ``OUTPUT``
- [same as input]
- Output vector layer with split lines or polygons from input
layer.
Python code
...........
**Algorithm ID**: ``qgis:splitwithlines``
.. include:: ../algs_include.rst
:start-after: **algorithm_code_section**
:end-before: **end_algorithm_code_section**
.. _qgissymmetricaldifference:
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.
.. include:: ../algs_include.rst
:start-after: **warning_attributes**
:end-before: **end_warning_attributes**
.. figure:: img/symmetrical_difference.png
:align: center
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**: :menuselection:`Vector --> Geoprocessing Tools`
.. seealso:: :ref:`qgisdifference`, :ref:`qgisclip`,
:ref:`qgisintersection`
Parameters
..........
Basic parameters
^^^^^^^^^^^^^^^^
.. list-table::
:header-rows: 1
:widths: 20 20 20 40
* - 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.
* - **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:
.. include:: ../algs_include.rst
:start-after: **layer_output_types**
:end-before: **end_layer_output_types**
Advanced parameters
^^^^^^^^^^^^^^^^^^^^
.. list-table::
:header-rows: 1
:widths: 20 20 20 40
:class: longtable
* - Label
- Name
- Type
- Description
* - **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.
Outputs
.......
.. list-table::
:header-rows: 1
:widths: 20 20 20 40
* - Label
- Name
- Type
- Description
* - **Symmetrical difference**
- ``OUTPUT``
- [same as input]
- Layer containing (parts of) features from each layer
not overlapping the other layer.
Python code
...........
**Algorithm ID**: ``qgis:symmetricaldifference``
.. include:: ../algs_include.rst
:start-after: **algorithm_code_section**
:end-before: **end_algorithm_code_section**
.. _qgisunion:
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.
.. figure:: img/union.png
:align: center
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.
.. figure:: img/union_with_overlay.png
:align: center
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**: :menuselection:`Vector --> Geoprocessing Tools`
.. seealso:: :ref:`qgisclip`, :ref:`qgisdifference`,
:ref:`qgisintersection`
Parameters
..........
Basic parameters
^^^^^^^^^^^^^^^^
.. list-table::
:header-rows: 1
:widths: 20 20 20 40
* - 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.
* - **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:
.. include:: ../algs_include.rst
:start-after: **layer_output_types**
:end-before: **end_layer_output_types**
Advanced parameters
^^^^^^^^^^^^^^^^^^^^
.. list-table::
:header-rows: 1
:widths: 20 20 20 40
:class: longtable
* - Label
- Name
- Type
- Description
* - **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.
Outputs
.......
.. list-table::
:header-rows: 1
:widths: 20 20 20 40
* - Label
- Name
- Type
- Description
* - **Union**
- ``OUTPUT``
- [same as input]
- Layer containing all the overlapping and
non-overlapping parts from the processed layer(s).
Python code
...........
**Algorithm ID**: ``qgis:union``
.. include:: ../algs_include.rst
:start-after: **algorithm_code_section**
:end-before: **end_algorithm_code_section**
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If you need to create a new substitution manually,
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.. |checkbox| image:: /static/common/checkbox.png
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