[OSM-dev] Massive building import - thoughts

sly (sylvain letuffe) liste at letuffe.org
Sat Feb 7 15:52:07 GMT 2009


Many thanks for all those usefull comments. 

> Assuming that most houses will have 4 nodes, you're talking about 
> importing roughly 10 million ways and 40 million nodes.

Given some quick manual checks :
here is a rather usual ~500 citizens village raster image:
( houses in orange )

French houses doesn't seams always rectangles ;-)
we could reach something like a 10:1 nodes/way ratio
Which gives us 10M ways and 100M nodes

> On the whole it seems to me that there is nothing to worry on the 
> database side, provided of course the import itself does not use too 
> many resources.

Sounds good.
For technical reasons : we don't have access to a vector file covering France, 
but a commune by commune exports from a rather poor WMS server. "communes" 
beeing admin_level 8 and there are currently 36 783 in france.
The first step might take form of a JOSM plugin (cadastre-fr) to convert 
buildings to OSM data and human organised checks to import.

> I would imagine some complaints from those users who are not interested 
> in buildings, 

This is our main concern, we could propose stripped out from buildings exports 
to those who don't want them to build map with.

But our main concerns is on a "osm mapper user experience" :
Given the current way main editors of OSM data, and API works, that would 
produce :
- a huge extra amount of unwanted data to download (so to say : delays)
- a more painfull mapping experience as mappers will have to draw their 
streets between buildings (and take care of editors's "helpfull" behaviour 
that wont be anymore on a high density layer)

That problems connects to discussion about API downloads striped out from ways 
on tag/values filters. (or with discussion about multiple databases)
While adding one more understanding difficulty to begginers.

The problem is not that simple, tests areas will be "built" in order to find 
what drawbacks we could hit.

Sylvain Letuffe liste at letuffe.org
qui suis-je : http://slyserv.dyndns.org

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