[Imports] Vermont Town boundaries from VCGI

Greg Troxel gdt at ir.bbn.com
Wed Aug 8 16:18:28 BST 2012

  > 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

  I plan to keep the existing state and national borders, and manually
  connect the new town boundaries with the existing state border.

I wonder where the existing data came from, and if the VCGI data is
actually better.

My impression is that the mass data is based on surveys of actual marker
stones, and when I've checked positions from (hiking class) GPS, I have
been unable to find errors that are beyond what I'd expect from GPS.  I
would expect the same of Vermont's data.

Calvin: what did you do about the state border when you imported the
town boundaries for Mass?  Leave it, or set it to the mass town border?

It might be best for you to make the Vermont town borders in OSM match
the official vermont data, and let the state border be different, until
this is figured out, rather than adjusting the town to match what might
be incorrect state data.  I don't see any real harm in them not lining
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