On 08/08/2012 07:15 AM, Greg Troxel wrote: > > I would suggest looking at the way town boundaries in mass are. I > believe that each boundary segment is a way, and town boundaries are a > relation. Is that what you are intending to do?
Yes. > Have you confirmed that the state boundary in osm matches the outer > boundary of towns? The state boundary in the VCGI file (which exactly matches the outer boundary of the towns in the VCGI file) does *not* exactly match the state boundary in OSM. In most cases involving straight lines it is reasonably close--within about 10 meters. In a few areas of the middle-of-the-lake border with New York, they diverge by over 100 meters. In on the river border with New Hampshire (the border is specifically the low water mark of the west bank of the river), there are some places where the river has shifted (e.g. to cut off an oxbow) and this is reflected in one version but not the other. There are also some places where the the two versions match but do not match the bing satellite imagery. Interestingly, on the US-Canada border, most of the nodes seem to be exactly the same--OSM has them marked with survey point reference numbers, so this would make sense--but shifted a few centimeters. Probably something to do with projections. I plan to keep the existing state and national borders, and manually connect the new town boundaries with the existing state border. > Is Vermont like Mass, in that every bit of land is in exactly one town? > > Do the Vermont state people think that the state boundary is exactly the > outermost town boundary, or is there somehow land in Vermont not in any > town? To the best of my knowledge--I don't have an authoritative source--every bit of Vermont is accounted for. Either it is a city or a town, which has a local government, or it is a township, gore, or grant, which doesn't have a local government. Each city or town sets its own boundaries in its town charter, but as I understand it in most(?) cases, that's in conjunction with a state law defining what it has to be. I haven't found official definitions of the boundaries of the gores, but the reading I've done (wikipedia) suggests that they exist, and match the boundaries of the adjacent towns (or adjacent gores). That said, each town does its own survey of the boundaries, and there have been disagreements about the results of the surveys. In the metadata of the VCGI file, it mentions a number of cases where neighboring towns have official maps that overlap or leave empty space. It also mentions that some towns aren't even using digital files for their official data. Thus VCGI has made an effort to provide its guess at the correct boundaries. From what I've seen, they've done a better job than anyone else. --Andrew _______________________________________________ Imports mailing list [email protected] http://lists.openstreetmap.org/listinfo/imports
