Is the prime meridian the starting line for measuring latitude?
No. The Prime Meridian is about Longitude, which was far more difficult to calculate than Latitude. Latitude can be measured by knowing how high the Sun is above the horizon & by the Stars at night. Longitude needs the addition of knowing time at one place & another place & speed & direction of movement. The Prime Meridian, 0 degrees Longitude runs from Pole to Pole through Greenwich, London. (The Headquarters of the Royal Navy at the time) 0 degrees latitude is the Equator.
