Advanced Placement (AP) Human Geography Practice Exam 2025 – The Comprehensive All-in-One Study Guide for Exam Success

Longitude measures the distance east or west from the Prime Meridian, which is established at 0 degrees longitude. The Prime Meridian runs through Greenwich, England, and serves as the primary reference line for geographical coordinate systems used for navigation and mapping. It divides the Earth into the Eastern and Western Hemispheres. This system of measurement is essential for determining the precise location of a point on the Earth’s surface and effectively communicates time differences as well, influencing time zones.

The equator, on the other hand, serves as the reference line for latitude measurements, not longitude. The International Date Line is an important line in terms of timekeeping that is located at approximately 180 degrees longitude but does not serve as a primary reference line for longitude itself. The Tropic of Cancer is a parallel of latitude located at approximately 23.5 degrees North, which is also unrelated to the measurement of longitude. The concept of longitude is fundamentally tied to the Prime Meridian, making it the correct answer.