# `gdal vector simplify-coverage`

Added in version 3.12.

Simplify boundaries of a polygonal vector dataset.

## Synopsis

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

    Simplify shared boundaries of a polygonal 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]
      -q, --quiet                                          Quiet mode (no 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 output is allowed
      --append                                             Whether appending to existing layer is allowed
                                                           Mutually exclusive with --upsert
      --output-layer <OUTPUT-LAYER>                        Output layer name
      --skip-errors                                        Skip errors when writing features
      --active-layer <ACTIVE-LAYER>                        Set active layer (if not specified, all)
      --preserve-boundary                                  Whether the exterior boundary should be preserved.

    Advanced Options:
      --if, --input-format <INPUT-FORMAT>                  Input formats [may be repeated]
      --oo, --open-option <KEY>=<VALUE>                    Open options [may be repeated]
      --output-oo, --output-open-option <KEY>=<VALUE>      Output open options [may be repeated]
      --upsert                                             Upsert features (implies 'append')
                                                           Mutually exclusive with --append

## Description

gdal vector simplify-coverage simplifies boundaries of a polygonal dataset, such that shared boundaries are preserved without introducing gaps or overlaps between features. Gaps or overlaps already present in the input dataset will not be corrected.

This requires loading the entire dataset into memory at once. If preservation of shared boundaries is not needed, gdal vector simplify provides an alternative that can process geometries in a streaming manner.

Simplification is performed using the Visvalingam-Whyatt algorithm.

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

Polygon dataset before (left) and after (right) simplification with gdal vector simplify-coverage.

Note

This command requires a GDAL build against the GEOS library (version 3.12 or greater).

### Standard options

--tolerance <TOLERANCE>

  Tolerance used for determining whether vertices should be removed. Specified in georeferenced units of the source layer.

--preserve-external-boundary

  Flag indicating whether to preserve (avoid simplifying) external boundaries. This can be useful when simplifying a portion of a larger dataset.

--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.

-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, --creation-option <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.

### Advanced options

--oo, --open-option <NAME>=<VALUE>

  Dataset open option (format specific).

  May be repeated.

--if, --input-format <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.

Note

However this algorithm is not natively streaming compatible. Consequently a in-memory temporary dataset will be generated, which may cause significant processing time at opening.

## Examples

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

    $ gdal vector simplify-coverage --tolerance=1 in.gpkg out.gpkg --overwrite

### Example 2: Using simplify-coverage as part of a vector pipeline

This can be used to make the output geometries have a consistent type.

    $ gdal vector pipeline ! read tl_2024_us_state.shp ! simplify-coverage --tolerance 2 ! set-geom-type --multi ! write out.gpkg --overwrite