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OSM Extract Polygon

codecov License: MIT

Changelog

Contributors: andgem, davetha, morandd

v. 0.5.0:

  • added administrative level information to the geojson output

Description

This small and simple tool processes OSM pbf files to generate boundary polygons.

The main question it answers is: How do I extract the polygon of an administrative boundary?

In particular it looks for administrative boundaries (e.g., city boundaries, country boundaries, ...) and creates an output file per boundary that is in the Osmosis Polygon format.

Since version 0.3.0 it also supports the GeoJson output format.

Download

Just head over to the Releases and grab the version for your operating system (macOS, Linux, and Windows supported).

Usage

Extracts administrative boundaries of OSM pbf files and produces polygon files compatible with Osmosis.

USAGE:
    osm_extract_polygon [FLAGS] [OPTIONS] --file <filename>

FLAGS:
    -g, --geojson      set this flag to generate geojson output
    -o, --overwrite    set this flag to overwrite files without asking; if neither this nor --skip is set the user is
                       being prompted should a file be overwritten.
    -s, --skip         set this flag to skip overwriting files; if neither this nor --overwrite is set the user is being
                       prompted should a file be overwritten.
    -h, --help         Prints help information
    -V, --version      Prints version information

OPTIONS:
    -f, --file <filename>          input file
    -x, --max <max_admin_level>    max administrative level (can take value from 1-11) [default: 8]
    -m, --min <min_admin_level>    minimum administrative level (can take value from 1-11) [default: 8]
    -p, --path <path>              path to which the output will be saved to [default: '<input_filename>_polygons/']

Example 1 - Simple use case

osm_extract_polygon -f karlsruhe-regbez-latest.osm.pbf

The program will create a folder <INPUT_PBF_FILE>_polygons/ in the same folder where the input file is. This folder contains for each administrative boundary it found and extract a .poly file. The name of the file is the name of the administrative boundary relation, potentially prefixed by a prefix defined in the relation under the tag name:prefix.

Should more than one administrative boundary result in the same name, then, to avoid overwriting files, the filenames will have postfixes that corresponds to the relation id the administrative boundary is based on. For example, it the result for data of Spain can result in the following three files: Vimianzo_12532173.poly, Vimianzo_348941.poly, Vimianzo_9482766.poly. For these 12532173, 348941, and 9482766 are the relation ids mentioned above.

For more information about the meaning of the minimum and maximum administrative level take a look into the OSM Wiki.

Example 2 - GeoJson Output

In the next example we will create, additionally to the *.poly output, also matching GeoJSON files. We do this by passing the command line parameter --geojson (or alternatively, the short form -g) to the program.

./osm_extract_polygon -f berlin-latest.osm.pbf --geojson -o

This should create additional GeoJson files in the subfolder berlin-latest.osm.pbf_polygons/. Note, that we have also passed the parameter -o which instructs the program to overwrite already existing files in this folder without asking.

Example GeoJson file in the output:

{
  "geometry": {
    "coordinates": [
      [
        [
          [
            13.441906929016113,
            52.3632698059082
          ],
          [
            13.440044403076172,
            52.363494873046875
          ],
          [
            13.437420845031738,
            52.36367416381836
          ],
          [
            13.437135696411133,
            52.36361312866211
          ],
          [
            13.436691284179688,
            52.36356735229492
          ],
          ...
        ]
      ]
    ],
    "type": "Polygon"
  },
  "properties": {
    "name": "Blankenfelde-Mahlow"
  },
  "type": "Feature"
}

Use Case: Extracting a smaller OSM file of a city

Assume you want to have a small OSM file of a single city. The problem you might face is, that the smallest file you can get is still very large. The tool Osmosis can extract parts of an osm file when supplied with a Osmosis polygon file, but you don't have such a file (and manually creating one is burdensome).

In this example I will explain how to solve this problem for the city of Karlsruhe, Germany.

Preparation

  1. Get the newest release of osm_extract_polygon from the release page.
  2. Install Osmosis
  3. Obtain a OSM pbf file that contains Karlsruhe: Go to geofabrik and download Karlsruhe Regierungsbezirk.

Execution

  1. Run osm_extract_polygon:
./osm_extract_polygon -f karlsruhe-regbez-latest.osm.pbf
  1. Verify that the program ran, a few hundred small *.poly files are in the folder karlsruhe-regbez-latest.osm.pbf_polygons/. The file you are interested in is Stadt_Karlsruhe.poly.
  2. Run Osmosis:
osmosis --read-pbf file="karlsruhe-regbez-latest.osm.pbf" --bounding-polygon file="karlsruhe-regbez-latest.osm.pbf_polygons/Stadt_Karlsruhe.poly" --write-xml file="karlsruhe.osm"

The output osm file you are interested in is karlsruhe.osm.