[OSM-talk] landuse=urban

[Chris Morley]

David Earl wrote:
>> On Saturday 10 Feb 2007 12:54, Tom Chance wrote:
>>> On Saturday 10 February 2007 12:18:28 Nick Whitelegg wrote:
>>>> What would be useful I feel is a generic tag for any urban
>> area, so that
>>>> urban and countryside areas can easily be distinguished. landuse=urban
>>>> seems a good choice. This would make it easy, for example, to draw an
>>>> urban area based on the Landsat or Yahoo imagery. 
 >>
>>> Just curious, what do we lack with
>>> landuse=residential/retail/industrial/etc? If people use those
>> then surely
>>> entire urban areas are clearly marked off? If there are urban areas that
>>> don't fit into those categories then we could expand the list.
>>>
>> The problem is that you might not know what is what, also it's
>> significantly
>> more effort (could involve creating 50 areas rather than just
>> one). If you're
>> using Landsat imagery or Yahoo imagery outside of the
>> high-resolution areas,
>> you can easily tell what's urban and what isn't, but little more
>> than that.
>>
>> That's not to say remove the finer-grained classification, but
>> marking out
>> whole urban areas with landuse=urban would make mapping which aims to
>> distinguish between urban and non-urban areas much easier to generate.
> 
> You could always underlay everything else in an urban area with such an area
> on layer=-5 say, then more specific things would show up on top.
> 
> However, I think there may be a way to do this automatically. Mst urban
> areas have large numbers of residential streets, and by determining a local
> envelope enclosing residential streets I think it might be possible to
> generate a suitable background. This almost happens anyway with abbutters
> egnerated for them, its justtehre are gaps, especially around roads one
> wants to classify as e.g. primary within the urban envelope. This wouldn't
> be perfectly accurate, of course, but would give the idea of a conurbation,
> or even just a small village.

Slightly off the point, but renderers should put the landuse tags below 
canals and rivers. You don't want a river disappearing when it enters an 
industrial area. (Currently Mapnik fails and Osmarender implementations 
are inconsistent). I know that the layer tag could be used to correct 
this. But then it is not a real indication of elevation, but is a 
renderer instruction. As a general point, these need to be kept out of 
the database if possible.

landuse=urban sounds like a reasonable feature which would be assumed 
(without having to specify a layer) to be rendered below almost 
everything else (except administrative areas and such like).