Description

Script to generate .POLY/.GPX files from OSM multipolygon relations.

Usage

0. Install libs from requirements.txt
1. Modify data/osm-borders.yml config file. Add countries with regions:
2. Run script

$> python osm-borders-to-poly.py

Output will be generated into data/poly folder.

Data format

Main config file data/osm-borders.yml contains list of countries with regions. Each region is defined by a set of OSM IDs.

How OSM relations are handled

osm-borders-to-poly expects that each OSM relation is a multipolygon. It downloads multipolygon data and glues it to a number or closed lines.

   *---[ Way 1 ]--*            --[Way 5]--
   |              |           /           \
   |              |          /             \
[Way 3]        [Way 6]      *               *
   |              |          \             /
   |              |           \           /
   *---[ Way 4 ]--*            --[Way 2]--

Imaging we have relation of 6 ways. And we need to extract 2 closed lines of it. First we need to extract all ways (instances BoardSegment class). And after that merge ways which have common points. Function mergeAreas is responsible for that. It builds a chain of ways where each next way starts where previous way ends. And because multipolygon in OSM could have more than one closed line, function mergeAreas returns list of such chains:

• Chain 1: Way 1, Way 6, Way 4, Way 3
• Chain 2: Way 5, Way 2

And the final step is to export points from those chains of ways into a single POLY/GPX file.