Thank you much, Perry. This is very helpful.
I have Garmin's MapSource Topo USA 2008 and National Parks East 24k (which actually covers some national forests too). I am lucky to live not too far from a National Recreation Area and a National Forest, so the 24K set covers much of my area. GPS or not, I always hike with full-size, printed USGS 24K topo maps and a compass - and a great deal of route preparation. In wilderness areas trails can appear and vanish, and their location on the map is officially an estimate (though a very good one).
Garmin's MapSource National Parks 24K is a good product, though I'd still
prefer rasters similar to USGS 24K maps. It does contain some inaccuracies but, evidently, not gross ones. I haven't worked with National Geographic or DeLorme but, in its own right, MapSource is fairly flexible and straightforward. The ability to export waypoints, tracks and routes to
Google Earth is a superb feature. Exported data is saved to "Temporary
places" in Google Earth, which you can then save to My Places. On tracks,
you can turn off data points to leave only the path traveled, or switch
off the path to leave only the points.
Topo USA 2008 is a defective product, as others have reported elsewhere. The position of most roads (but not all) is slightly offset. While
traveling / walking on a road you are almost always shown as being
somewhat off road unless you zoom to >=500 feet or set the unit to lock on roads. Also, roads are shown with a similar offset vis-a-vis the terrain.
Fortunately, when viewing a track, the path of travel is shown correctly
in MapSource (though the road-terrain offset still holds). That is: points
selected in MapSource may be a little off-target in real life but data
collected by the GPS receiver usuall looks right in MapSource. I have been
using GeoPDFs and Google Earth to determine desired waypoints, then creating them in MapSource.
GeoPDFs are geo-referenced 24K quadrangle maps in PDF format available for free download from store.usgs.gov. (Entire USA covered). They work with a Geo toolbar available free from www.terragotech.com
. You set the datum and coordinate format, and then you can see the exact USGS 24K coordinates for any spot. (Most paper 24K maps are NAD27 CONUS datum but the GeoPDF can be set to WGS 84). You can also enter coordinates and have the GeoPDF find the spot. It also allows you to measure line and path distances. Map resolution is decent but not great, about the same as normal USGS maps and, usually, you cannot mark waypoints etc. on them for upload. The most recent release of the toolbar allows for importing .gpx files but I have not had luck making this work. I'll get in touch with Terragotech support.
Many trails - but not all - are shown on GeoPDFs. Many are also shown on
Garmin's 24K maps but there are some inaccuracies there too. Paper maps from the U.S. Forest Service are 24K and show trails as accurately as possible, but they are not available in digital format. I am considering
scanning some segments and then using 3rd party software to geo-reference the scans. Also to see if the maps can be uploaded to the GPS receiver. This is a lot of work, though. Hence, for the time being, I plan to mark waypoints on the paper map, identify them carefully on a GeoPDF and create the actual points for download on MapSource. I was just wondering whether National Geographic or DeLorme showed trails more accurately than Garmin - it appears that they do have advantages over MapSource.