[GIS] Getting list of all countries using Overpass API

djangoopenstreetmapoverpass-apipython

I'm a developer that's trying to build a django application and trying to incorporate the Overpass API to it. I'm new to the API and OpenStreetMap (and GIS in general), so I thought I would start off by getting a list of all of the countries and build from that.

However I've searched online and nowhere does it mention how to do this with the API, can someone show what query does this?

Best Answer

The Overpass Turbo query for a list of all countries is

[out:csv("name:en")];relation["admin_level"="2"];out;

You can get it from the command line with

 overpass-api.de/api/interpreter?data=%5Bout%3Acsv%28%22name%3Aen%22%29%5D%3Brelation%5B%22admin_level%22%3D%222%22%5D%3Bout%3B%0A

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I would use the area feature of the Overpass API in order to achieve this goal.

[out:json];
area
   ["name"="France"]
   ["boundary"="administrative"]
   ["admin_level"="2"];
(._;(pivot:);>;);
out body qt;

Lines 2-5 are selecting the correct area.

Line 6 creates an union consisting of:

the area itself
the pivot element of this area (the relationship/way/... from which this area was generated)
the ways/nodes referenced by the pivot element

Line 7 just prints out the results. The qt parameter is just a performance optimization and not necessary (http://wiki.openstreetmap.org/wiki/Overpass_API/Language_Guide#order_attribute)

By setting admin_level to 2 you can make sure, that you will only get national borders. You will need to adapt this value in order to get different types of boundaries. A list of the meaning of admin_level's values can be found at http://wiki.openstreetmap.org/wiki/Admin_level#admin_level.

By the way: Areas are created by the Overpass-API server and are not part of the original OpenStreetMap database. Internally, the Overpass server is doing exactly what scai wrote: It is gathering together the data from relationships. (see wiki.openstreetmap.org/wiki/Overpass_API/Areas)

[GIS] OSM server tiles and Overpass API

Overpass API needs its very own database because it has to perform very different queries compared to a tile server. Likewise if you intend to set up a geocoder (e.g. Nominatim) you will also need a different database for the very same reasons.

It's all about performance optimization. Usually these services are deployed on different physical systems so that's not a problem. Theoretically it would be possible to use a single database for all services but that would be horribly slow.

Best Answer

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