[OSM-dev] Massive building import - thoughts

Frederik Ramm frederik at remote.org
Fri Feb 6 22:29:49 GMT 2009


sly (sylvain letuffe) wrote:
> In france, next to the cadastre's agreement of using their data for OSM, we 
> might soon be able to import something like 60% of France's builings.

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

We currently have about 304 million nodes and 25 million ways. Your 
import would raise that to 344 million nodes and 35 million ways; 
looking at the recent development, you would be importing half a year's 
worth of normal OSM growth within, perhaps, a month or so.

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.

Your import would have a node:way ratio of 4:1, whereas the current data 
has about 12:1 (after the import it would be 9:1). This is probably not 
a cause for concern. You would be importing about 80 nodes per square km 
on average. France would jump from 5 million nodes total to 45 million 
nodes total, from an average of 10 nodes per square km to an average of 
90 nodes per square km. The Dutch are already at 100 nodes per square 
km, and I don't hear them complain, so it seems that such a data density 
can be handled sufficiently by the existing tools.

I would imagine some complaints from those users who are not interested 
in buildings, and for whom 90% of the data they download is useless 
after the import. You might have to provide filtered extracts for them.


Frederik Ramm  ##  eMail frederik at remote.org  ##  N49°00'09" E008°23'33"

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