What is the starting point for latitude?

The starting point for latitude is the equator, which is located at 0 degrees latitude. Latitude lines are horizontal ways to measure how far north or south a location is from the equator. They run parallel to the equator, increasing in degrees to the North Pole at 90 degrees north and to the South Pole at 90 degrees south. This system allows for precise location tracking on the Earth's surface in relation to the equator, which serves as the fundamental baseline for all latitude measurements.

The other choices represent different concepts. The prime meridian is the starting point for longitude, not latitude. The Arctic Circle and the Tropic of Cancer are specific latitude lines, but they are not the reference point for measuring latitude, as they are located at 66.5 degrees north and 23.5 degrees north, respectively.