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[aprssig] Re: Earthmate Delorme

KC2MMi kc2mmi at verizon.net
Fri Jun 24 01:01:53 UTC 2005


<< I'm 1000 feet away from it.  I think it's because
of using a wrong datum when they imported the additional roads into Tiger.>>

Drew, this is a known issue. The US Census Bureau suggests you write
Congress to let them know that the TIGER maps are grossly incorrect in many
places, and the Census has no budget to correct them. The Census Bureau also
states unequivocally that the TIGER maps are NOT SUITABLE FOR NAVIGATION or
precision use of any kind, they are meant for demographic comparisons only.
They are trying to upgrade and each year a number of counties (often 100+)
are updated to WGS84 but for now...anyone using TIGER maps for navigation is
likely to find rude surprises that change on county borders. And with the
annual TIGER updates.

DeLorme once stated that they did not have atlases for some states (they
used to be paper map publishers) because it cost too much to obtain the data
directly from some state sources. Other states supplied it for less, or
there was more demand for them. So, I wouldn't be surprised to find DeLorme
also has used different map sources. Remember, if you are using any map for
navigation and their is no datum referenced on the map--you can't trust it.

There are some other "gotchas" on some online sources. Maptech's online map
server mixes map from different datums--with no notice about which are being
used. Caveat emptor and all that good stuff.





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