Memory is used to load detailed topographic maps, street-level maps, or additional waypoints into your GPS receiver. Detailed maps can use a great deal of memory on your device, so you need to consider how much internal storage capacity your device has. Higher end GPS devices also usually accept a memory card for additional storage. You can also share data easily between different GPS units of your own, or with a friend if you are using a memory card. There are several sizes of memory cards to choose from to expand the memory of your GPS navigation system. Most are between 1 and 4 GB of memory; although, you can purchase larger or smaller memory cards than this if you are interested, depending on how you plan use your GPS units.