[Talk-us-massachusetts] Talk-us-massachusetts Digest, Vol 45, Issue 3

[Greg Troxel]

Leaving aside the consensus process and alignment, I see two points  as
both quite valid, although contradictory:

  Wayne's point that the MassGIS  dataset is the data of record for
  boundaries

  Yury's point that for boundaries that are defined by rivers, when the
  actual river location is clearly different from the MassGIS data, OSM
  should have data that is more accurate


In thinking about this, I have a number of questions that I think need
answering:

  (There is probably some datum fuzz going on, in terms of NAD83/WGS84
  confusion, and I'm trying to figure that out for other reasons.  We
  should keep that in mind, but I don't think we are getting things
  right at the sub-meter level and I think that the mismatch from
  MassGIS data and imagery that Yury is pointing out is well more than a
  meter.)

  In MA, only licensed surveyors can "authoritatively determine"
  municipal boundaries, says MassGIS.  I suspect that this is in the
  same sense as determinging parcel boundaries, not drawing them on a
  map and am willing to go with that interpretation.

  Town boundaries are set by state law.  We're a bit out a limb here as
  far as really looking up the statutes and/or things in the Atlases.
  I'd like to pick a good example -- perhaps Yury can suggest one --
  where the river is quite different from the MassGIS data.  But the
  MassGIS data is coded to say 'boundary is the river', and I don't see
  any reason not to take that at face value.

  There is some notion of "center".  Law is complicated about that and
  we should understand what it means.  My fuzzy understanding (not to be
  used for reasoning) is that center in MA means the points equidistant
  from the shore/water line when the water is at "normal" height.  If we
  use imagery, that leads to another meter or so of fuzz (unknonw
  height) on top of the imagery datum fuzz and the imagery alignment
  fuzz.  I am ok with not worrying about this, because we are delusional
  about better than 3m absolute accuracy for tracing river centerlines
  anyway.  I suspect we can achieve 5m.

  Town boundaries are very much a thing dealt with by the selectmen of
  the two (or more) towns.  While being defined in statute, each town
  has an obligation to visit the stones, and if any are missing, to
  jointly with the other town straighten it out.  So I really wonder if
  there is some record of the water boundary that is agreed to by the
  two towns, or not.  I am guessing not.

  MassGIS seems to have just drawn lines from imagery.  If so, then
  their drawing isn't necessarily any better than ours.  But it is easy
  to ask if there is more to it.  I will write to them, and report back.



If anyone knows people in town governemment in a town with a river
boundary and is willing to call them and ask how this really works, that
would be really useful.  My town doesn't have river boundaries (there is
a lake, but the boundary is set by coordinates in law).  Besides, if
anyone called my town and asked a question like this, the town would
tell them to call me :-)

Greg