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I just received an email from National Geographic, advertising "At Last: Nat Geo Maps on a GPS Device!" This is rather interesting, in view of the following history -
Some 20 years ago, several companies introduced software for PCs and Apples to display scanned USGS topographic maps. In the lat 1990s, as civilian handheld GPS receivers became available, several of the manufacturers added vectorized topographic maps. The scanned maps are so-called "raster scans" and reproduce the map as a series of pixels, more or less a "photographic" reproduction of the map. Raster maps use a DEM (Digital Elevation Model), which is a grid of specific elevation points, then use a "contouring" algorithm to draw the contour lines. The disadvantage of the raster maps is that you are limited in how much you can magnify the map before seeing the individual pixels. With a vector map, you have unlimited magnification, but the contour lines, water boundaries, roads, and other features are often pretty far off because of the crudeness of the grid used (the USGS DEM models are a 100 meter grid at best, and 1 km in some areas - lots can happen in 100 m, like a major 2000 ft cliff in Yosemite Valley).
Lots of the original companies have vanished. One of the best, Wildflower, eventually merged with National Geographic, which continues to publish TOPO! (disclosure - I did some consulting for Wildflower and later NatGeo). While TOPO! and some other computer maps can exchange some information with GPS receivers, people have wanted better maps on the GPSRs. Magellan, Lowrance, Garmin, and Delorme all include vector maps (some models are "political features" only - that means roads, streets, boundaries; while some include topographic vector maps).
Now here is the interesting thing about the NatGeo "At last!" email. A couple years ago, Magellan and NatGeo announced a series of GPSRs onto which you could load TOPO! topographic maps. These were raster maps, with a very fine scanning resolution. So this is not the first time that there has been a GPSR that could load TOPO! maps. One of the unique features is that NatGeo is offering memory cards with the maps loaded, making installation pretty simple.
Unfortunately, Magellan was having some financial difficulties and got traded among several corporations, at least a couple of which were VC companies looking for a quick way to make money. So maybe the "At last!" means that NatGeo, being a pretty stable and large non-profit has some more direct control over the product. At this point, I do not know who the actual manufacturer of the Active 10 TREK GPS is.
In the meantime, Garmin has made available their own proprietary scans of USGS maps to load on their GPSRs, as has Delorme. Magellan, under their new owners (MiTAC, a Taiwanese company that produces several lines of GPSRs and other navigation gear), has reorganized and introduced several new GPSRs that look very competitive (disclosure - I have received a Magellan 610 for evaluation, as well as a Delorme PN-60/SPOT combination unit, also for evaluation). There are also map hacks available in the geocaching world to scan various maps yourself (such as local county park maps) and load them onto your own unit. The GPSR manufacturers have expressed mixed feelings about these map hacks, being torn between the very large customer base in the geocaching world (literally tens of millions of cachers worldwide) and the risks of people hacking into their proprietary products. They cooperate with the geocaching hackers, but also state "your warranty is voided" if you do this, and issue a strong reminder that their technology is patented, copyrighted, and otherwise protected legally.
Hopefully, I can do a writeup comparing these various units, without running into too much problem with the Fundamental Law of Electronic Widgets ("By the time you select your electronic product, pay the cashier, and head out of the store to your car, there will be at least two new updated versions with dozens of new features and significantly upgraded performance")