I don’t spend much time on field equipment, e.g. GPS units.  Why?  Lack of interest?  No.  Lack of space in my job description.  Yes, I know.  A GIS Manager who doesn’t have a GPS is it’s own category of silly.  None-the-less, when a colleague told me that Garmin now has firmware support for custom maps for some of it’s GPS units, I told him it might be a good choice for his field work and that I’d work on loading our maps onto his unit when it came in.

Sure enough, it came in, and we’ve loaded them.  You can follow Garmin’s directions, but if you already have georeferenced data, skip them and by whatever means you know, generate a jpeg with a world file (for you ArcMap users, goto data view, file:export choose jpeg, and check the world file checkbox).  You can export an image from any desktop or server package, and if you know the upper left coordinate of the image, and the pixel size, you have enough to create a world file.  Easiest hand crafting of geographic data you can imagine (it’s the gateway for bigger and better hand crafted geographic data).

Now, you can use MapTiler to generate the kind of KMZ that is so near and dear to the garmin’s heart.  Just choose KMZ as your output type, choose one of the garmin types in the next screen, and the rest easy easy GUI fun.

Limitations:

Well, Garmin doesn’t want you to load more than 100 tiles (probably for performance reasons), but what does that mean practically?  For the testing I did, that meant for a 4 foot pixel (most of our best data isn’t more spatially accurate than that, even if it’s more precise), I was able to load about 3200 acres– enough for one of our larger parks.  Good enough for our work, but you might consider a deeper tool if you need more raster data than that at a time.