matt on 28 Mar, 2019 06:51 PM
Web maps like CalTopo's are traditionally broken up into 256x256 pixel tiles; this is the size used for MBTiles exports (which are accessible on the same page). Garmin places limits on the number of images you can have in a KMZ file, and each image can be up to 1024x1024 pixels - since the page is used for both KMZ and MBTiles, it will show your download as X images and 16*X tiles.
KMZs do not support multiple zoom levels, Garmin will resample up to a certain point but stop showing the layer if you zoom too far in/out.
Garmin limits you to 100 images, don't know if there is a correlation below that between performance and # of images loaded.