Hi,
have a look at posts #5 and #8 .... you will find which is the map for mapsource and wich one for device..... But yes ,the link above your post relates to mapsource.
Erdas is a system and powerful authoring software for geospatial datas WW , i didn't understand your question (my fault,sorry ) but .... how it can be related/compared to a Garmin basemap ? There is a fundamental difference between these progs.
Have a nice day, Umbe