Get building polygon using reverse geocoding

[VasinYuriy]

I need to search for a building polygon.
I'am using this query and it works fine most of the times:
https://nominatim.openstreetmap.org/reverse?lat=55.823131&lon=37.497309&format=geojson&polygon_geojson=1
But sometimes, my coordinates are pointing exactly at shop within building:
https://nominatim.openstreetmap.org/reverse?lat=55.619467&lon=37.50928&format=geojson&polygon_geojson=1
In that case, polygon is not returned. I have tried to add layer=address parameter, but that does not help.

I am about to install my own nominatim server, so, maybe there is a way to import only buildings or solve this problem by some configuration trick?

[lonvia]

Reverse geocoding tries to return the most specific result it can find. A point in a building is considered more specific than a building. That's why you get the shop. The shop does have an address, which is why it matches the layer=address. In this specific case, however, the address is inherited from the building outline. We probably should exclude POIs with inherited addresses from the address layer.

[lonvia]

Done, see #3700. Your example now returns the mall building when used with layer=address:

https://nominatim.openstreetmap.org/reverse?lat=55.619467&lon=37.50928&format=geojson&polygon_geojson=1&layer=address

Note that this only works as long as the addr:* tags are really on the building, When addr:* tags are on nodes, then you still get the node returned. Nominatim cannot inherit towards building polygons yet, see #2926 among others.

(I've presumed here that you are not really interested in building polygons without any address. Please, correct me if that assumption is wrong.)

[VasinYuriy]

Thank you very much! Actually, i do interested in building polygons that do not have any address. But that is not a problem, i will just make second request with layer=address if first request returned a point. Needless to say that this is a rare case, actually.

[lonvia]

Nominatim doesn't store building polygons when they have no other interesting tags. Mostly this is to save space. There are 640 million buildings in OSM at the time of writing. That's about 3 times the number of objects that Nominatim indexes in total.

If you want to get all buildings, you indeed need your own Nominatim instance and customize your import style. Start with one of the standard styles and modify it too unconditionally import buildings, like that:

local flex = require('flex-base')

flex.import_topic('address')
flex.set_main_tags{building = 'always'}

Also, if you only do the reverse lookups, consider importing with --reverse-only to save a bit of space.

[VasinYuriy]

Thank you! I will try this.