I’m new to this so my apologies if this is a naive question, but I haven’t been able to find an answer by searching.
When I look at the OSM data for New York I see that buildings always have heights. For example:
But when I look at a place like Palo Alto, CA I don’t see heights associated with buildings:
And when I look at Palo Alto in a 3D viewer like f4map, I see that the buildings have heights, and varied heights, but I’m not seeing it in the OSM data I’m exporting from the same map area from https://www.openstreetmap.org/.
Different people mapped the two cities and/or there is suitably licensed height data for New York. (If nothing else, most buildings in New York may be old enough that copyright has lapsed on sources of height data.)
Whether buildings even get mapped at all depends on the interests of local mappers. Most mappers won’t map heights. Personally, I consider that it is more important to get the street number than even the building outline.
I believe Los Angeles also has building height data, but San Franciso where buildings were imported does not.
Usually height data have been derived from Lidar, so access is needed to a decent Lidar survey. Increasingly local govt bodies are sharing this data: but it’s a hell of a lot to incorporate into OSM for one city let alone worldwide.
F4 and other tools which use Simple 3D building tags may make use of building:levels: something which it is often relatively easy to add to buildings across swathes of a city. Alternatively OSM is a wiki so using a rule of thumb (e.g., residential buildings are 3 m / level, office buildings 4-5 m /level may provide a reasonable first cut).