I received a PM from the Adirondack Forum today that said:
"...I just bought the Garmin 60CS. I have a question about the maps. Do I need the Garmin Mapsource United States Topo or... the one from National Geographics Topo that I think is better for hiking? If I don't buy the Garmin Mapsource Topo, can I download maps in my GPS?..."
This question comes up so often that I felt obligated to post an answer here. The answer is no, you cannot load National Geographic TOPO! maps onto any GPS. You can however, create waypoints and routes with TOPO!, and transfer these to your GPS, but not the maps. Let's look at why not, and what kind of maps you can load onto your GPS.
The National Geographic TOPO! maps look just like a paper map from USGS (example above, at right). That's because they are scanned images, also known as raster imagery. Since they are scans, they have a pretty big file size. That's why it takes 10 CDs to cover the state of California. And that's one of the main reasons that GPS manufacturers have taken a different approach.
Instead, most GPS receivers utilize vector maps, like the one on the left. This appears to the user as an image, but it is really created from a data file rather than an image file. It is made up of lines and points, so it requires much less space than a raster (image) file. The vector map at left is from Garmin's MapSource US Topo, and yes, this is what you need to put topo maps on a Garmin mapping receiver. All these products are proprietary, so you'll need Magellan software to put maps on a Magellan GPS.
There are always exceptions though, and you can make your own maps for most models of GPS receivers, avoiding the need to buy proprietary software. It's not a fast process, but there are step-by-step directions in my book, along with chapters on programs like National Geographic TOPO! and much, much more. Finally, my publisher would be displeased if I didn't tell you that you can get GPS Mapping direct from them or from Amazon.