My confusion results from the fact that my custom maps are not .kml. The custom maps I've been making for my old GPS (RINO130) are vector maps transfered to the receiver as .img files. I can still do this with my new GPS (RINO650) but I can also add a .kmz raster map. There is also some confusion because .kmz is a sort of meta file, i.e., it is a file of files. It can hold vector information as well as raster information. In fact it can hold links and instructions to load other information. (The attached .kml file will load several raster layers of information about modeled snow conditions that may be interesting. I have unziped it so it can be examined as text to get an idea of how it works.) I don't think you can load a vector map into a Garmin receiver as .kml. It must be .img as far as I know. When I want to see both my custom map and the Garmin map I'm referring to my custom vector map and the Garmin vector base map. I have always held onto my GPS receivers until they were far out of date. Long after receivers with maps were available I was using one without. I did this by making paper maps which were far superior to the low resolution, slow updating, B&W maps that were available at the time. My son, the physicist, wrote a program that made a downloadable track that formed a grid, as if someone had walked a boustrophedonic (Google it) path. With this grid on my GPS receiver and also on my custom made paper map I was able to navigate quite well. In fact I still use this technique because the paper map is so much easier to read than the small screen. I have a 13'x19' photo quality printer. I never did use any purchased maps, preferring to construct my own from publicly available data. I found that in the process of constructing my own map I came to understand the terrain pretty well before going out. When I did get a GPS receiver that would hold maps I found a way to load the maps I was making to print. This is a long explanation for why I use the term 'custom map' in the general sense of any map, electronic or paper, designed and constructed for a specific purpose. To Garmin 'basemap' is for the map that comes standard in the receiver, 'custom' is for anything else. 'Mapset' seems to refer to vector maps. Just a few days ago I bought a new Garmin receiver and with your help I have been learning the terms Garmin uses to market their maps. They could do us a big favor by introducing their customers to the difference between vector and raster maps and using those terms in their marketing. This is a free, private forum and opinions posted by its members do not necessarily reflect those of Trailkeepers of Oregon. Hiking is a potentially risky activity, and the entire risk for users of this forum is assumed by the user, and in no event shall Trailkeepers of Oregon be liable for any injury or damages suffered as a result of relying on content in this forum. All content posted on the forum becomes the property of Trailkeepers of Oregon, and may not be used without permission. Source.