In France, cadastre is the most official source about buildings and land ownership. When you buy/sell a building all the documents refers to the cadastre.
It provides sometime too many details compared to what could be seen by survey. Does this mean it is wrong to have too many details ? Considering merging these detailed outlines automatically into a single block is not a option because in many cases in cities this would lead to a single building outline for a whole street block loosing way too many details. Bing aerial pictures are most of the times a good source, but not the reference. Cadastre data may be more up to date (we have new buildings not visible on Bing), and sometimes it is the reverse when Bing aerials are from 2011 or even 2012. That's usual with different source of information, that's why I indicate bing year in the source tags when I trace over bing. I manually traced building in a village in Burgundy because the cadastre was only raster there at that time, then the vector version became available. I updated the whole area and found that vector was much more accurate and higher quality than what I did manually. I think it is the case most of the time because of the georeferencing that is done manually and because inaccuracies/lack of details in the manual tracing. One important thing when tracing cadastre by hand is that you cannot cross check with Bing at the same time because of different projections (Lambert vs Mercator). So cross check with Bing must be done afterwards, exactly like when using vector data. That's why I consider manual tracing as a waste of time, and not high quality compared to using extracted building from vector data. Buildings, even with some artifacts like the one showed by Frederik example, are helping a lot adding POI at their right position. This is also something I learnt after adding POI in my own city and then adding buildings from vector extraction when it became available (this summer). I add to relocate a lot of POI added by myself and other contributors, and adding new ones is now much easier. -- Christian _______________________________________________ talk mailing list [email protected] http://lists.openstreetmap.org/listinfo/talk
