For computation, you might use double fractional degrees, or radians. For display, you usually display as integral degrees, minutes and seconds (or second.fractions of seconds) of arc.

A GPS unit can calculate the current longitude by triangulating satellite signals. In the days of sailing ships, determining longitude depended on having an accurate clock so that you could compare the time of day from observing the sun with the time back home at the prime meridian.

There are commercial databases so that you can guess the longitude of a server from its IP.