I'm a little bit confused about your statement that you made a .kmz and tried to load it into Google Earth. Generally, you *make* the .kmz with google earth. What are you creating the .kmz with?
Is tiling required in order to break the map down into the 1024x1024 resolution for Garmin devices?
Yes, the 1024x1024 tile is a Garmin "limitation". Garmin used to have a page detailing these limitations, but for some reason I'm having trouble pulling it up at the moment. You could google "Garmin Custom Map limitations" to read more.
The general idea is to follow these steps:
- find a map you like
- convert the map to .jpg and into the projection that GoogleEarth likes (this is where I have spent much time and effort)
- georeference the map by creating an Image Overlay in Google Earth (generally easy if your map has control points)
- export that image overlay as a .kmz
- use a "map tiler" to cut that image into a bunch of tiles that will automatically georeference each tile for you based on the larger image
- copy that "tiled" .kmz into your CustomMaps folder
I did provide you with a tiled .kmz in this thread, if you wanted to check it out.
I did find that many tilers were hosing my carefully crafted images (adding compression artifacts to the image), so be careful.