# `gdal vector geom simplify`

Added in version 3.11.

Simplify geometries of a vector dataset.

## Synopsis

    Usage: gdal vector geom simplify [OPTIONS] <INPUT> <OUTPUT> <TOLERANCE>

    Simplify geometries of a vector dataset.

    Positional arguments:
      -i, --input <INPUT>                                  Input vector datasets [required]
      -o, --output <OUTPUT>                                Output vector dataset [required]
      --tolerance <TOLERANCE>                              Distance tolerance for simplification. [required]

    Common Options:
      -h, --help                                           Display help message and exit
      --json-usage                                         Display usage as JSON document and exit
      --config <KEY>=<VALUE>                               Configuration option [may be repeated]
      --progress                                           Display progress bar

    Options:
      -l, --layer, --input-layer <INPUT-LAYER>             Input layer name(s) [may be repeated]
      -f, --of, --format, --output-format <OUTPUT-FORMAT>  Output format ("GDALG" allowed)
      --co, --creation-option <KEY>=<VALUE>                Creation option [may be repeated]
      --lco, --layer-creation-option <KEY>=<VALUE>         Layer creation option [may be repeated]
      --overwrite                                          Whether overwriting existing output is allowed
      --update                                             Whether to open existing dataset in update mode
      --overwrite-layer                                    Whether overwriting existing layer is allowed
      --append                                             Whether appending to existing layer is allowed
      --output-layer <OUTPUT-LAYER>                        Output layer name
      --active-layer <ACTIVE-LAYER>                        Set active layer (if not specified, all)
      --active-geometry <ACTIVE-GEOMETRY>                  Geometry field name to which to restrict the processing (if not specified, all)

    Advanced Options:
      --if, --input-format <INPUT-FORMAT>                  Input formats [may be repeated]
      --oo, --open-option <KEY>=<VALUE>                    Open options [may be repeated]

## Description

gdal vector geom simplify simplify geometries, ensuring that the result is a valid geometry having the same dimension and number of components as the input.

The simplification uses a maximum distance difference algorithm similar to the one used in the Douglas-Peucker algorithm.

This done by the `OGRGeometry::SimplifyPreserveTopology()` method which preserves the topology per feature, but not for a whole layer. Thus gaps or overlaps between geometries that were initially contiguous may happen.

This command can also be used as a step of gdal vector pipeline.

Line dataset before (left) and after (right) simplification with gdal vector simplify.

Note

This command requires a GDAL build against the GEOS library.

### Standard options

-f, --of, --format, --output-format <OUTPUT-FORMAT>

  Which output vector format to use. Allowed values may be given by `gdal --formats | grep vector | grep rw | sort`

--co <NAME>=<VALUE>

  Many formats have one or more optional dataset creation options that can be used to control particulars about the file created. For instance, the GeoPackage driver supports creation options to control the version.

  May be repeated.

  The dataset creation options available vary by format driver, and some simple formats have no creation options at all. A list of options supported for a format can be listed with the --formats command line option but the documentation for the format is the definitive source of information on driver creation options. See Vector drivers format specific documentation for legal creation options for each format.

  Note that dataset creation options are different from layer creation options.

-lco <NAME>=<VALUE>

  Layer creation option (format specific)

--overwrite

  Allow program to overwrite existing target file or dataset. Otherwise, by default, gdal errors out if the target file or dataset already exists.

--active-layer <ACTIVE-LAYER>

  Set the active layer. When it is specified, only the layer specified by its name will be subject to the processing. Other layers will be not modified. If this option is not specified, all layers will be subject to the processing.

--active-geometry <ACTIVE-GEOMETRY>

  Set the active geometry field from its name. When it is specified, only the specified geometry field will be subject to the processing. Other geometry fields will be not modified. If this option is not specified, all geometry fields will be subject to the processing. This option can be combined together with `--active-layer`.

--tolerance <TOLERANCE>

  The specified value of this option is the tolerance used to merge consecutive points of the output geometry using the `OGRGeometry::SimplifyPreserveTopology()` method The unit of the distance is in georeferenced units of the source layer.

### Advanced options

--oo <NAME>=<VALUE>

  Dataset open option (format specific).

  May be repeated.

--if <format>

  Format/driver name to be attempted to open the input file(s). It is generally not necessary to specify it, but it can be used to skip automatic driver detection, when it fails to select the appropriate driver. This option can be repeated several times to specify several candidate drivers. Note that it does not force those drivers to open the dataset. In particular, some drivers have requirements on file extensions.

  May be repeated.

## GDALG output (on-the-fly / streamed dataset)

This program supports serializing the command line as a JSON file using the `GDALG` output format. The resulting file can then be opened as a vector dataset using the GDALG: GDAL Streamed Algorithm driver, and apply the specified pipeline in a on-the-fly / streamed way.

## Examples

### Example 1: Simplify geometries using a tolerance of one km (assuming the CRS is in meters)

    $ gdal vector geom simplify --tolerance=1000 in.gpkg out.gpkg --overwrite