For large distances, however, latitude observations greatly improve the accuracy of large maps built up from many small maps. Latitude observation becomes a significant practical skill for travellers and for administrators of large kingdoms. The kingdom of ancient Egypt existed in a narrow strip along the Nile River. Knowing latitude meant knowing where in Egypt one was. The vertical grid lines on a map indicate longitude.
Longitude is a standard for locating a precise position on Earth.
Like latitude, longitude is measured in units of angle, so it is a standard based on geometry, not depending on any socially or legally agreed unit of distance, such a mile or a kilometer. A more serious difficulty with longitude is that determining longitude by astronomical observation is more challenging problem, requiring not only the measurement of star positions, but accurate timing. Alexander's, the Roman and the Islamic empires. The first reasonably accurate map of the Mediterranean region and the Near East was made by the great astronomer Ptolemy. We'll learn more about longitude in connection with the later empires.