Fixing Polygons in OSM
There are many different ways (multi)polygons in OpenStreetMap can be mapped correctly and there are even more ways in which they can be mapped incorrectly. Of the over 260 million (multi)polygons in OSM more than 100,000 contain mapping errors of one kind or another and about 250,000 are tagged old style (with tags on the outer ways instead of on the relation) making multipolygon tagging and processing much more complicated and much more expensive than it needs to be. But this is not only about multipolygon relations, it is also about polygons created from closed ways. They also can and do have errors.
We are trying to fix all this and this web site is here to organize this effort.
When we have finished this effort, mapping will be easier, because there will be only one canonical way of tagging multipolygons. Editors can take this into account and help mappers in better ways. And it will make using the data easier and faster because the programs (such as Osm2pgsql and Osmium) converting OSM data into multipolygons for rendering or other uses can be simplified. It will also make it easier to detect mapping errors raising the quality of the OSM data.
Read this for many more details:
- Background on (multi)polygons
- Typical problems with OSM multipolygons
- Frequently Asked Questions (FAQ)
- Some notes about rendering
There are many ways of helping with this effort depending on your OSM skill level and time. Read this to get you started fixing things.
To see what the map would look like if we removed old style multipolygons, you can use our comparison map.
There are some areas in central Europe with a lot of (or larger) old style multipolygons. Some other clusters can be seen here: Finland, Georgia, USA, New Jersey, USA, Romania, around Toronto, Canada.
The statistics help us track what has been done and what still needs to be done.
- Spatialite database containing information about all problems found in OSM areas. (About 1 GByte). Get this QGIS project file and put it in the same directory as the areas.db file and run qgis area-errors.qgs.
- Sqlite database containing daily statistics on areas in OSM. (Small file)
- OSM PBF file containing only old-style multipolygons, ie relations tagged only with type=multipolygon with all dependant ways and nodes. (About 270 MBytes)
- A shapefile with all ways contained in the file above, so these are the geometries of all ways that are members of old-style multipolygons. (About 410 MBytes)
- OSM PBF file containing all ways and multipolygon relations that are broken in some way. (About 300 MBytes)
If you have any questions or want to contribute in any way, here are some ways to get in contact:
- Open an issue on our github repository.
- Discuss on the OSM developer mailing list.
- Join us on the #osm-dev IRC channel on OFTC (how to get there).
This effort is organized by me, Jochen Topf. You can also contact me personally, but I prefer you'd go through one of the channels above.