What are lines of longitude used for besides mapping the earth?

Lines of longitude play a crucial role in determining time around the world. This is because longitude is directly related to the Earth's rotation. Each line of longitude corresponds to one hour of time difference, which is why the concept of time zones is based on longitudinal divisions. For instance, as the Earth rotates, different areas experience sunrise and sunset at different times. The Prime Meridian, located at zero degrees longitude, is the starting point for coordinating time internationally. Areas to the east of the Prime Meridian are ahead in time, while those to the west are behind.

Although determining geographic locations is also a critical function of lines of longitude, the primary and direct relation of longitude with time makes it more relevant in this context. This contrasts with measuring altitude and calculating distance, as those aspects involve different geographic principles, such as elevation above sea level and the use of coordinate systems or scales, respectively. Thus, latitude and longitude are primarily used for mapping and locating points on the Earth's surface, while longitude specifically connects to the global time system.