Garmin handheld GPS units use vector graphics to display imagery, so it’s generally been considered impossible to view raster imagery on them, like USGS topo maps or aerial photographs. But I’ve figured out a way, and created a program that lets you convert free USGS topo maps downloaded from the Seamless Server, black-and-white DOQQs, color satellite imagery, any georeferenced raster imagery, to a Garmin-compatible format: Moagu – the Mother Of All GPS Utilities. Rich Owings has the first review at GPS Tracklog (he likes it!).
Here’s a few screenshots from my Garmin 60Cx:
You can download a demo version at the website. Introductory price is $19.95.