Creating the graticule

The idea of using a system of intersecting lines to locate features on a map existed almost from the inception of systematic mapmaking. As early as the third century BCE, Chinese mapmakers put reference lines on their maps, but they didn't apply the technique to the entire earth. In fact, there is no evidence that they recognized the earth was a sphere.

The first person credited with tackling the problem of locating surface features on a spherical earth was our friend, Eratosthenes. Eratosthenes devised a system of north–south and east–west oriented lines encompassing the earth's surface and intersecting each other.

In the second century BCE, a Greek astronomer and geographer named Hipparchus refined and formalized the system. His system is the same one we know today as latitude and longitude. The system of latitude and longitude, also called parallels and meridians, is based on 360 degrees. Each degree is divided into 60 minutes and each minute into 60 seconds. The 360-degree Babylonian system for dividing a circle or sphere, including the heavens, was already in use by the ancient Greeks. Hipparchus had the foresight to apply the system to the earth's surface.

Latitude lines are parallel, run east and west around the earth's surface, and measure distances north and south of the equator.

Longitude lines run north and south around the earth's surface, intersect at the poles, and measure distances east and west of the prime meridian.

The network of intersecting lines of latitude and longitude is called the graticule. It is imaginary on the earth, of course, but is drawn on globes and maps for reference.

The graticule of latitude and longitude lines is an angular measurement system. All features on the earth's surface are located using measurements that are relative to the center of the earth. Latitude lines are parallel to each other while longitude lines converge at the poles.