Which line indicates the starting point for measuring Longitude?

The prime meridian serves as the starting point for measuring longitude. It is defined as 0 degrees longitude and runs from the North Pole to the South Pole, passing through Greenwich, London. Longitude lines, also known as meridians, are measured in degrees east and west of the prime meridian, extending up to 180 degrees in each direction. This system of measurement is crucial for navigation and mapping, allowing for a standardized reference point to locate positions on the Earth's surface.

In contrast, the tropic of cancer and the equator are important reference lines for measuring latitude rather than longitude. The tropic of cancer lies at approximately 23.5 degrees North latitude, marking the northernmost point where the sun can appear directly overhead. The equator serves as the 0 degrees latitude line, dividing the Earth into the Northern and Southern Hemispheres. The International Date Line, located at approximately 180 degrees longitude, is the counterpart to the prime meridian for determining time zones but does not serve as a starting point for measuring longitude.