[OSM-dev] determining the boundaries of cities?

[Ákos Maróy]

Martin,

> It is not as easy as it sounds like. Actually we often do not have
> this information (directly) in OSM. What you could do is:
> * use the landuses and extend them slightly (to also get the streets,
> which are sometimes enclosed in the adjacent landuse but actually
> shouldn't).

yes, this is what I tried

> * You could also use residential roads and extend them (draw a hull
> around them).

I was considering something like this as a last resort :) but yes, when
looking at a map generated from OSM, visually it's quite clear where
city boundaries are - where the streets stop :)

> * Last but not least you should look for polygons tagged with
> place=town/city. These are IMHO actually the bounds of the settlement
> (but mostly that's nodes, not polygons in current OSM).

I looked at this, and these are usually points for Hungary, marking the
center point of the city.

>> One possibility seemed to be to go with:
>> boundary = administrative && admin_level = 8
> 
> -1, as you already discovered, these are administrative boundaries and
> not what you are looking for.

well yes, but then again, a proper administrative boundary would be fine
with me.

> yes, we have quite incomplete data for city extensions as a polygon.
> One of the reasons is IMHO, that the main mapnik map uses external
> data for builtup areas (from natural earth), so people are less aware
> that there is something useful missing.

I see. so basically what is not natural, is considered to be man-made?


Akos