The ID has to be a number that no other map file that you'll be using in conjunction with this one has. The name field is what shows up when you add a map to be uploaded in Mapsource, and also will be displayed on your GPS. If this is just one big map, name it something descriptive like "Minnesota Trail Map". If your map will have different regions, use this field to describe the region. I have 6 regions for my Minnesota map, and this one happens to be the North West.

Set "RGN limit" to 1024. For "TRE size", a higher number (in the neighborhood of 5000) will give you a smaller file size but will make the map perform more slowly on your GPS. A lower number (500-1000) will make a bigger file but it'll be much faster on your GPS. 1000 was a good number for my map. If yours is less detailed, you can increase it.

You can set your map to be transparent, which allows your map to be drawn over other maps in your GPS. If it's not transparent, it will hide the other maps from view. Transparency is a good option if your map only has trails on it. That way people can overlay the trails on top of Garmin Topo map series or any of their other products. If your map has roads and water, it's better to make it not transparent, or else it might look a bit sloppy and confusing.

I'm no expert on this part, but these settings worked for me. For Preprocessing, "Generalization Only" is fine if you don't have routing information.

Click OK, save your map, then do File > Export > Garmin IMG / cGPSMapper.exe. Select where you want to save your .img, and then click on "Run". cGPSMapper will do its thing, which could take anywhere from a few seconds to a few hours depending on the speed of your computer and size and complexity of your map.

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