Map and Coordinate Discussion
As you might gather from this travelogue as well as other web pages
that I have authored on trips and hikes, I am a bit of a gps to map
freak.
With the National
Geographic Map that I have reproduced in parts, they say that the
the map datum is NAD27. The map has UTM grids drawn on it. My GPS
normally is set to a datum of WGS84. I changed the datum to NAD27
Central, and UTM coordinates, but was unable to really get good
overlays to the map. The GPS would at worst only be off by 100 feet,
and for example on the Rio Suerte, our launch point and lunch landed
nowhere near the river.
maps.google.com uses the WGS84 datum. When I changed the GPS back to
WGS84 and put coordinates in that datum into maps.google.com, the
results were much better. Google itself does not have Costa Rican maps
on line, but it does have satellite photos. On the kayak on the Rio
Suerte, when I put the coordinates into maps.google.com, I ended up
right on the river. I then matched the satellite location to the
National Geographic Map, put labels on, and put on the web page.
This page maintained by Don Samuels
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This page last updated January, 20, 2007