Creating Garmin Custom Map MVUMs

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My Garmin Oregon 450 GPS displaying a portion of the Hahns Peak / Bear Ears Ranger District MVUM. If I had taken this picture while on the trail, a small blue triangle would indicate my current position and heading on the map. Click image to enlarge.

Creating Garmin Custom Maps from Georeferenced MVUMs

Once you've created a georeferenced motor vehicle use map (MVUM), Global Mapper can be used to create a .kmz file containing a custom map that can be used as a background layer in Garmin Colorado, Oregon, and Dakota GPS units. Maps are installed by connecting the GPS to the computer and dragging the created .kmz file to the custom maps folder on the GPS unit.

One caveat: most Garmin GPS units are limited to a total of 100 1024-pixel by 1024-pixel tiles for all maps installed on the device and, while the custom maps feature can be turned on and off, individual maps cannot be turned on or off. It's all or nothing. The net result is that even with a very large micro SD card in the GPS, you're likely only to be able to load a single MVUM on the GPS at a time.

Requirements

Creating the .kmz File in Global Mapper

The first big step in getting a georeferenced MVUM into a Garmin GPS unit is to create a .kmz file that is compatible with the GPS. Fortunately, Global Mapper makes this easy. Here's the procedure:

Launch Global Mapper.
Click "Open Your Own Data Files" on the opening screen.
Use the open file dialog box to open the .zip file containing the georeferenced TIFF file for the MVUM. The .zip file should contain a .tif file and a .tfw file.
Global mapper will open and display the MVUM.
Select GPS -> Send Raster Maps to Connected Garmin Device. Don't worry if the GPS isn't connected at this point. We'll save the file to your computer then copy it to the GPS later.
The presented dialog box has lots of options split into two tabs. Here are a few tips for setting these:
- I generally use the default values calculated by Global Mapper for sample spacing / resolution.
- If I want to change the resolution, I click the "Click Here to Calculate Spacing in Other Units..." button and usually use meters. I've found 10-15 meters per pixel to be useful for MVUMs but sometimes those values can exceed the 100 image tile limit of the GPS.
- I almost always set the export bounds to "All Loaded Data" but if I'm interested in a smaller portion of the MVUM, I'll zoom the area of interest to fill the screen and use the "All Data Visible On Screen" setting instead.
- See the screen captures below to see the rest of the settings I use in the Garmin Options dialog box.
Click OK.
Use the Save As dialog box to name and save the generated .kmz file some place convenient. You'll need it to download to the GPS.
Optional: open the .kmz file in Global Earth to see your handiwork superimposed on the Earth.

Downloading the .kmz File to the Garmin GPS

The next step is to copy the .kmz file to the custom maps directory on the GPS. Here are the required steps:

Connect the GPS to the computer using a mini USB cable. Windows should automatically install the device drivers for the GPS and the GPS should display a picture of itself connected to a computer.
The GPS appears to the computer as a storage device similar to a USB thumb drive. Double click on the Computer icon on your desktop to display the drives attached to the computer.
My GPS appears as "Garmin Oregon (K:)" as shown below. Yours should appear somewhat similar but with possibly a different name or drive letter. Sometimes my GPS doesn't appear in the Computer Folder. The solution is to unplug the GPS from the computer, pull the batteries out, leave them out, then reconnect the GPS to the computer.

My GPS appear as "Garmin Oregon (K:)" in Windows Explorer. Click image to enlarge.
Double click on the icon for the GPS.
Double click on the Garmin folder.
Create a new folder called "CustomMaps" inside the Garmin folder if this folder does not already exist.
Double click on the CustomMaps folder.
Drag the .kmz file you created previously into the CustomMaps folder.
Disconnect the GPS from the computer and replace the batteries if you removed them.

Enabling Custom Maps on the GPS

The final step is to enable the display of custom maps on the GPS.

Turn on the GPS.
Once the GPS is powered up, select "Setup" then select "Map" then select "Map Information."
Select "Disabled - Custom Maps" then select "Enable."
Now the display should have a box that says "Enabled - Custom Maps" followed by the filename of your .kmz file.
Tap the return arrows and exit the settings screen.
Tap the Map icon.
You should now be able to use your finger to scroll to the geographic area that the MVUM covers and see the MVUM displayed on the GPS. If the MVUM is not displayed, you may need to zoom in or out using the + and - icons.
That's it! Now get out from in front of the computer and get outdoors!

Notes

Here are some additional notes and clarifications on the process:

Most software capable of generating a .kmz Google Earth file can be used to create Garmin custom maps—including Google Earth!
Custom maps are limited to 100 1024-pixel by 1024-pixel tiles on most current Garmin GPS units.
All custom maps loaded on the GPS must total less than 100 1024x1024 pixel tiles—even if they're in separate files and you have gobs of storage space.
Garmin also has a procedure to create custom maps using only a JPEG image of the map and Google Earth. While less expensive than using Global Mapper, it's also less accurate.