On Sep 26, 2012, at 7:44 PM, Richard Weait wrote: > I think that "drawing all of the nodes and points manually" is an > important difference, from a quality point of view. Each node or way > that you draw by hand, is carefully considered and placed, one at a > time. It isn't perfect; nothing is. I suggest that this leads to a > kind of automatic quality control, as the nodes and ways are placed.
Hi Richard, I agree that it's an important difference, but you can see it also the other way around : since the the raster based process is manual, it's more error prone. For instance, it's easy to forget a building, a street, misinterpret the image, forget to set a tag (name, source…), introduce inaccuracies of a few meter, not to mention that some raster maps are not geo-referenced (or badly). I have been there :-) So the 2 processes have different sources of errors, and as you say, only a careful and manual review can provide the quality we all except. This point is clearly made on the french pages on the Wiki. > My conclusion, is this. The quality of the hand drawn nodes and ways > will be better because when we draw the nodes and ways by hand they > get more individual attention and care than when we start with a group > of nodes and ways from another file. I don't agree there. The 2 processes have different errors, but it's hard to say that one is globally better than the other (in terms of quality). > I consider what you describe as the raster process to be an import > when the quantity of data is large. The raster process relies on an > external data source for a large quantity of information. If that > source is used without considering additional data sources, I think > that the classification as import is very clear. Yes, I agree. But it doesn't pertain to the normal cadaster import process, because no one is supposed to import from the cadaster only. The wiki is really clear about that (french only, sorry): https://wiki.openstreetmap.org/wiki/WikiProject_Cadastre_Fran%C3%A7ais/Import_dans_OSM#Qualit.C3.A9_des_donn.C3.A9es And what I have seen this is the way mappers work too. > On the other hand, I think that if the quantity of data is small, if > multiple sources are considered with appropriate weight, and if local > knowledge or an in-person survey is included as well? Then the > description might be closer to "really good mapping." You are describing 2 ends of a scale very well. Currently we are in-between, but nearer to the second one, because we have multiple sources (uploaded GPS tracks, Bing, existing OSM data, and usually the mapper's own GPS tracks and knowledge). The point is that with the time, we tend to go even further in the direction of the second one, because more and more data is available in the OSM database and we tend to get more sources, not less. NB: just FYI and completeness: there are actually 25% of the maps vectorized according to this page: https://wiki.openstreetmap.org/wiki/WikiProject_Cadastre_Fran%C3%A7ais _______________________________________________ talk mailing list talk@openstreetmap.org http://lists.openstreetmap.org/listinfo/talk
