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[cdt-l] gps?



If you look at a USGS map closely, you'll notice all kinds of little
details in the contour lines. These small details can often help you
distinguish one hillside from another, or pinpoint your location more
precisely. The TOPO USA CDs are "vector based", which means their maps
are drawn from a database which contains geographic information at
specific latitude/longitude points. For example, the database may
indicate that a particular geographic point is "7200 feet elevation",
has a small creek flowing through it, and is forested. The software then
"connects the dots" and interpolates the areas in-between the points to
draw a map. If the points are close enough together, the resulting map
would be identical to the USGS 7.5 minute map. But, sometimes, the
points are not close-enough together & what looks like a smooth hillside
on the TOPO USA map may contain all sorts of small ripples and ridges
that are only visible with the USGS maps.  All that said, the TOPO USA
philosophy is a good approach, I think... it's a more versatile format -
it can easily be updated and re-formatted. Plus, it's easy to make
custom maps that way (you can add or leave-out certain data). I think
it's the future of mapping, but it's not quite "there" yet.  I'm not
sure where the TOPO USA people got/get their source data, or how it
was/is entered into their database. I e-mailed them about it, but only
got back a lame "marketing fluff" response.

-Jonathan

-----Original Message-----

On Sat, 15 Mar 2003 05:48:48 -0000, Jonathan Ley <jonathan@phlumf.com>
wrote:

> ... The TOPO USA CDs are really a neat product, but they lack the
> resolution needed to navigate the CDT (many of the subtleties of the
USGS
> maps are "smoothed-over" in the TOPO USA CD set). ...

Jonathan, can you explailn a little more what you mean by
"smoothed-over"?
Thanks.