What is GPS Ephemeris Data
GPS ephemeris data is used by your GPS devices (smartphone, GPS running watch, camera with built in GPS tagging etc.) to predict which satellites will be in the sky at a particular point in time. Knowing which satellites are available dramatically decreases the amount of time it takes for your device to get a GPS “fix”. The prediction data is usually valid only for a few days so new data needs to be downloaded from the internet periodically.