Which meridian is considered the starting point for measuring longitude?

The Prime Meridian is the correct starting point for measuring longitude. It is defined as 0 degrees longitude and runs through Greenwich, England. This meridian serves as the reference line from which all other longitudes are measured both east and west. By establishing the Prime Meridian, navigators, cartographers, and geographers have a standardized point from which to reference longitude, allowing for more accurate navigation and mapping.

The Equator, on the other hand, is used as the baseline for measuring latitude, which focuses on north and south positioning rather than east and west. The International Date Line is not a meridian for measuring longitude but serves as the fictitious line that indicates where one day ends and the next begins. The Arctic Circle is also unrelated to longitude; it marks the latitude region in the Northern Hemisphere where, at least once a year, there is a 24-hour period of continuous sunlight or darkness. Thus, the Prime Meridian is uniquely established as the foundational line for measuring longitude.