I downloaded the entire N. Am. map. There was not enough internal memory space to upload only the 48 states to the RT. I could have uploaded only a region of the states, but did not go that way. I don't remember how many MB the map was. I have a 16GB SD card, way more than I need. It works fine. I read in one of the Garmin pages the recommended Zumo size SD is 8GB. I have the map, MP3's, and some images on the SD card.

 

There are several HD dealer POI files you can load into a Garmin GPS. I logged into Garmin web-site, there is a link to POI URL's. I found one and loaded it into my Garmin branded GPS using their POI loader.

Here is a URL to download POI files for about anything you want including HD shops

http://www.poi-factory.com/poifiles

Here is a link for HD dealerships
http://www.poi-factory.com/node/1995

 

Here is the instruction that I have followed to install maps into the SD card in my Zumo550.