On Sat, Jul 3, 2010 at 5:06 AM, Toby Murray <toby.mur...@gmail.com> wrote: > I just downloaded the Kansas extract from cloudmade: > http://downloads.cloudmade.com/north_america/united_states/kansas > > After rendering I noticed that the northern border was missing. > Looking at it some more, the extract seems to be cut off about a half > mile too far south. The cutoff for the other 3 borders looks to be > about a half mile or so outside of the border which is fine, it is > just the northern border that is off. I suppose the other option is > that the extract is correct and the state boundary is off in OSM... > Can anyone confirm either of these theories?
Neither is correct. At least, not with absolute accuracy. But the state boundaries in OSM come from TIGER, and usually are pretty darn close — certainly better than a half-mile error. CloudMade has been doing these extracts since before OSM imported state boundaries from TIGER. (Before that, state boundaries could be inferred by county boundaries, which had been imported from USGS. That particular boundary source can at times be a half mile off...) I actually don't know where CloudMade gets its state boundary polygons for the purposes of data extracts. It's probably not a very detailed polygon, anyway. Here's a suggestion for CloudMade: When creating these boundary extracts, use a generous state boundary polygon that gets an extra margin all around the state by a few miles. Then, look for the actual state boundary multipolygon in that data. If it's a closed figure with no errors, then use that to further trim the dataset. (If not, optionally, use the last error-free version of the state boundary multipolygon from previous extracts.) Since these are only done once a week, this shouldn't be too huge a processing load. -- David "Smith" a.k.a. Vid the Kid a.k.a. Bír'd'in Does this font make me look fat? _______________________________________________ Talk-us mailing list Talk-us@openstreetmap.org http://lists.openstreetmap.org/listinfo/talk-us