There’s something about a topographical map that gets me in the mood for an adventure. More than a typical highway map, a topo goes off road, detailing the hidden valleys and mountain passes accessible only to those willing to brave the briars on foot — or fatbike. Half the fun of an adventure is the anticipation of it anyway, and a poring over a topo map starts you dreaming about what’s possible.

The natural companion to a topo map used to be a compass, and it’s fun to still carry one along for old times sake, but the topo’s modern mate is a GPS unit. Not only does a GPS unit pinpoint your precise location on the globe, it can also carry a variety of basemaps over which you can navigate tracks or routes. My Garmin eTrex 30 came with a basic global basemap and I added the U.S. Topo 100K for an extra fee. The “100K” designation describes the map’s level of detail. And it’s really pretty good for your typical romp though the woods. If you’re looking to zoom in a little more, though, you’ll want to seek out a 24K version — usually more expensive for less geographic coverage.

BUT, if you’re willing to spend a little time manually converting digital topo maps into the standard GPS “.kmz” format, you can save some money and take your pick from a variety of map options. The absolute best source for digital topo maps online is the U.S. Forest Service website, where you can download free, up-to-date 24K quality topos of any National Forest in the U.S.

Once you’ve converted the files to the correct format you can load them into BaseCamp, Garmin’s free desktop mapping tool, then create tracks, routes, and waypoints, and even upload the Forest Service maps into your GPS unit itself. You’ll want to keep in mind that the Forest Service maps are “raster” as opposed to “vector” which means the file sizes will be quite a bit larger than the topos you can purchase from Garmin. Some prefer the smoother, hand-drawn feel of the raster USFS topos over their more digital looking vector cousins anyway. Depending on the speed of your computer and GPS unit, manipulating the images can feel a bit sluggish at times.

Since the Ouachita National Forest is practically in my backyard, and home to some of the greatest mountain biking and hiking trails in the region, I recently undertook the project of converting topos of the entire forest into the Garmin-readable .kmz format. It took some trial and error but the final product works like a charm. For those of you interested in working on your own nearby National Forest, here are a couple tips …

Start by going to the Forest Service maps page and selecting your desired state. You’ll have the option of downloading pdfs or geotiffs for each region of a forest — go with the geotiffs. These files already have all of the necessary global positioning metadata embedded, so once you get them into BaseCamp they’ll know exactly where to show up on the globe.

The next step is to download a copy of gRaster onto your PC. Yes, unfortunately Mac users are out of luck on this one. I’m a die hard Mac user myself, and I had to stoop the level of using Bootcamp for this part of the project. gRaster is a fantastic program, though, and well worth fiddling with Windows for. It shrinks/crops your raw geotiff into a usable size and then converts the geotiff into a .kmz file. You can even run a compression algorithm on the file before the final conversion to save a little space. Works like a charm and worth the $5.

Finally, you’ll drop the .kmz files onto a “list” in BaseCamp, create a new track, and start planning your next adventure.

Of course, if your next adventure happens to be somewhere in the Ouachita National Forest, the work has already been done! Here are the files. Each .zip file contains a number of .kmz files. You’ll need to decompress the .zip and then drop the .kmz’s onto a new “list” in Basecamp. Got it? (249 MB) (265 MB) (274 MB) (223 MB) (193 MB) (170 MB)