[OSM-talk] All you've ever wanted to know about the french cadastre

[Paul Norman]

> From: Vladimir Vyskocil [mailto:vladimir.vyskocil at gmail.com]
> Subject: Re: [OSM-talk] All you've ever wanted to know about the french
> cadastre
> >  The larger part of cadastre data
> > is just dumped into the data base never to be touched again by any
> mapper.
> 
> That's also wrong, the french community has developed some very powerful
> tools like osmose.openstreetmap.fr which is used to automatically
> discover many errors from cadastre and others, it's used along the
> import process by many people to locate and fix many bugs, for example
> here is a search focused on some errors that we seek :

Sarah's numbers come from Nominatim and the statistics for France and are
based on most of the imported buildings not having other tags added to them.
Because I have a pgsnapshot database at home I can do a more detailed
analysis to evaluate what percentage of cadastre buildings have been touched
since they were uploaded, looking at any change, even the addition or
deletion of nodes.

There are 28.7 million building=* ways with one of the top 5 cadastre source
values on http://taginfo.openstreetmap.org/keys/source#values. Of these 17.9
million are version=1. 62.2% of cadastre building ways are never touched
again by any mapper. Sarah is correct and the majority of imported buildings
are never touched.

Aside: Because 18% of the ways in the database are from the French cadastre
generating these stats requires a sequential scan of the ways table and
really makes me with I had an array of SSDs.