From the Manufacturer:
For simple and accurate recording of time and location information, Canon's compact GPS Receiver GP-E2 is the perfect complement to the EOS System. The GP-E2 records location information such as longitude, latitude, elevation, direction and Universal Coordinated Time (UTC) as EXIF data, while also serving as an electronic compass on camera or off. Versatile connectivity options include USB and hot shoe connections with the EOS 5D Mark III and the EOS-1D X (USB connection only with the EOS 7D); smart design and rugged construction ensures reliability plus the ability to be used as a standalone GPS recorder. The newest GPS system designed specifically for the EOS system, the GP-E2 is an ideal tool for photographers on the move.
Rugged, Lightweight Design
To be able to endure a photographer's travels, Canon designed the GP-E2 to share the same rugged and durable exterior construction as the EOS 5D Mark III DSLR body while still remaining compact and lightweight. Able to withstand harsh weather conditions, the GPS Receiver GP-E2 is a great enhancement to the EOS 5D Mark III for those who wish to take their EOS system out into even the most remote environments.
EXIF Location Recording
When in use, the GPS Receiver GP-E2 will automatically record the geographical information (latitude, longitude, altitude, and Universal Coordinated Time (UTC)) of videos and photos. Detecting altitude is even possible from inside an airplane or helicopter.
Note: In certain countries and regions, the use of GPS may be restricted. Therefore, be sure to use GPS in accordance with the laws and regulations of your country or region. Be particularly careful when traveling outside your home country. As a signal is received from GPS satellites, take sufficient measures when using in locations where the use of electronics is regulated.
Acts as Standalone GPS Logger
Additionally, the GP-E2 can be used as a standalone GPS logger. It can be carried in its included case or users can wear it comfortably on their waist. The location information is automatically stored on the GP-E2 at specific intervals and logged information can be added to the EXIF information at a later time using the supplied Map Utility.
On-Board Electronic Compass
There's also a built-in electronic compass that can accurately detect the cardinal direction in which the photographer is facing - even if the EOS 5D Mark III and EOS-1D X are held vertically, the GP-E2 can still record the proper positioning from when it is in a normal position.
Syncs with Camera Time via Built-in Atomic Clock
Accurately adjusting the cameras internal clock with the GPS Receiver GP-E2 is easy because it can use the UTC (Universal Coordinated Time) with a margin of error of about ±0.01 second on the EOS 5D Mark III. The margin of error when used with the EOS-1D X is ±0.02 second. Event photographers will find the transmitter's GPS Time Sync Function quite helpful because it can set and synchronize the internal clocks in multiple cameras. This function is not available when using the GP-E2 with the EOS 7D.
AA Battery Powered
The GPS Receiver GP-E2's uses readily available AA batteries, so users can easily power up the receiver without worrying about recharging; AA batteries are also widely available because they can be found almost anywhere around the world. And because the GP-E2 has its own power source, photographers can still get hours of continuous use with the camera because the GP-E2 will not drain the camera's battery.
Hot Shoe and USB Connectivity
The GPS Receiver GP-E2 can be attached to the camera body via the hot shoe on the EOS 5D Mark III and the EOS-1D X, or USB terminal with the EOS 5D Mark III, the EOS-1D X and EOS 7D.