Tag the building or the property?

Hi all: I’m new to OSM, and it’s totally sucked me in.

I’m tagging all the fire stations in my area, and it’s raised a general question: for something like a fire station - which could have multiple buildings - which thing is the fire station? I can think of several approaches, and I didn’t know how to look for it.

Assume I can outline the entire property - which is what I think of as the fire station - as well as individual buildings.

  1. Which is amenity=fire_station: the property, or the main building? Each building?
  2. Which has the address: the property, or the main building? my guess: the building
  3. Is there any value in capturing the property boundaries at all?
  4. In the event of multiple buildings for one fire station, is it possible that relations are in play here?

I like the idea of having building outlines, but I’m trying not to think about what looks good in the renderer.

What are best practices for this kind of thing? I’m trying to be consistent and provide the max metadata to the maps.

Some examples:

Fire Station #53 - whole property outlined

Fire Station #54 - just buildings


  1. I would suggest to only tag the property as amenity=firestation.

If you tag the individual buildings as well, there is a high chance of multiple cluttering firestation “icons” and name labels appearing, as it is difficult for a renderer to determine if a building is within a “property” tagged with the same tag, unless GIS wizardry is applied, senselessly consuming already limited CPU processing power / render time.

Only in case there is no noteworthy property, or you don’t know the property outline, you could tag (one of) the building(s) itself (and thus not adding a property outline).

  1. Renderers generally don’t do much with “relation” information, except for multipolygon relations, as relations are rather difficult constructs to deal with. In case there are multiple firestation buildings on the same property, you may consider creating a single multipolygon for all of them, thus allowing a single firestation icon and label to be assigned during render time. However, this is only sensible if you don’t intend to do micro tagging, assigning individual functions to each building. Of course, you could still “tie” everything together with some custom (non-multipolygon) relation, but unless you thoroughly document this on the OSM wiki, or follow an already established practice documented there, the value of it will be limited, because it may not be clear what the relation represents. You may wish to discuss this with fellow OSM’ers first.

This was very helpful, thank you, not just for the direction, but for the rationale.

Also see the OSM aiki about http://wiki.openstreetmap.org/wiki/One_feature,_one_OSM_element in general.