The SanDisk Class 4, the Lexar Professional 633x SDHC, the Lexar High Performance MicroSDHC 300x and the Kingston Digital Class 4 microSDHC are four good SD card options for GPS navigation devices. All four are available on Amazon.com, and each has received 4.5 stars out of five from hundreds of customers.
The Class 4 and the 633x SCHD are SD cards, and the other two classify as microSD. Refer to the manual of your navigation device to determine the SD card type that is compatible with your device. If unsure, both of the microSD cards come with microSD-to-SD adapters, but may perform more slowly when connected through an adapter.
Around 4 gigabytes of storage space is enough to install maps of North America. As all four cards offer 16 gigabytes of storage, they can hold multiple maps of North America, or other continents in addition to NA. After installing the maps, slide up the lock switch on the memory card to secure the map data.
The SanDisk and Kingston cards are Class 4 cards, but Lexar's cards are Class 10. Class 4 cards can transfer 4 megabytes of data every second, and Class 10 cards can transfer 10 megabytes per second. Although all four are fast enough for navigation devices, installing new maps to the cards by Lexar takes less time.