The map is divided up into tiles, which are roughly 2 degrees longitude by 2 degrees latitude. Above the map the number of tiles required to create the current map view is shown.
Your membership level dictates how many tiles may be used to construct a map for your GPS unit. For example if your tile allowance is four, then the largest map that may be copied to your GPS unit will consist of four tiles.
The current membership levels are (keep in mind that a single tile can cover up to 80x80 miles):
Sponsor memberships are available from Cache Zone.