[OpenLayers-Users] Reprojection: Maps not lining up

[Matthew Pettis]

Hi,

I am using Openlayers with Mapserver to show a shapefile of roads in
MN that are in epsg:26915 and allowing users to toggle between that
and Google Maps (spherical Mercator projection per
http://spatialreference.org/ref/user/google-projection/).  I use
mapserv.exe and a .map file to reproject the MN roads into the Google
projection, and when I toggle between them, the extents *almost* match
up.  It appears that the MN roads extent covers a slightly larger area
than the Google Maps extent.

I don't know if this is an OpenLayers or Mapserver question, but I'm
thinking it is a Mapserver one.  Can anyone tell me why the extents
*almost* match up?  I would think that they would either match up
almost exactly (or at least in a tolerance that I cannot tell by the
naked eye), or I would have messed up my transformations, and it would
be completely out of sync.  Is it a function of disparities in the
data that I cannot fix, or are there fine tunings that I can adjust to
compensate?

Thanks,
Matt

--
It is from the wellspring of our despair and the places that we are
broken that we come to repair the world.
-- Murray Waas