Latitude and Longitude

Latitude and longitude is a common geographic coordinate system which allows us to locate ourselves or other features on a map. It is used worldwide for navigational purposes on topographic maps, nautical maps, and road maps. It is also used in many GPS systems associated with phones, cars, boats, airplanes, military applications, firefighting, and tracking movement of tectonic plates, just to name a few. The latitude and longitude system is standardized so that a person from Mexico can easily communicate their location to a person in Africa or Europe, without any concern for potential language barriers.

Latitude, or parallels, represent how far north or south of the equator a point is on earth, measured in degrees, from 0° at the equator (00° 00’ 00”), to 90° at the poles (Figure 2.9). Each degree is divided into 60 minutes (‘), and each minute can be divided into 60 seconds (“). Lines of latitude remain the same distance apart as they circle the earth.

Equator separates the northern hemisphere from the southern hemisphere. — **Figure 2.9**: The equator divides the northern from the southern hemisphere. Additional lines of latitude are indicated (CC-BY 4.0; Chloe Branciforte and Cynthia Lampe, own work).

When specifying a latitude, always state whether it is in the Northern Hemisphere (N) or Southern Hemisphere (S). For example, Half Dome in Yosemite National Park is located at 37° 44’ 46” N latitude, read as 37 degrees, 44 minutes, and 46 seconds North latitude. This latitude does not locate Half Dome exactly, since this line of latitude encircles the entire globe north of the equator; we need to examine the other half of the coordinate system, longitude.

Longitude, or meridians, represent how far east or west a point on earth is from the Prime Meridian (up to 180°). The Prime Meridian, 0° 00’, 00” longitude, is a north-south line that runs through Greenwich, England. As they near the poles, lines of longitude become closer and closer together (Figure 2.10). Much like lines of latitude, each degree is divided into 60 minutes (‘), and each minute can be divided into 60 seconds (“).

Prime Meridian separating the eastern hemisphere and western hemisphere. — **Figure 2.10**: The Prime Meridian divides the eastern and western hemisphere. Additional lines of longitude are indicated (CC-BY 4.0; Chloe Branciforte and Cynthia Lampe, own work).

When specifying a longitude, always state whether it is in the Western Hemisphere (W) or Eastern Hemisphere (E). For Half Dome, the longitude is 119° 32’ 4” W longitude, read as 119 degrees, 32 minutes, and 4 seconds West. Half Dome is in the Western Hemisphere, between the Prime Meridian in the east and the 180th meridian in the west. Note that the International Date Line (IDL), where the day changes, roughly corresponds to the 180th meridian.

Together, Half Dome can precisely be located at, 37° 44’ 46” N, 119° 32’ 4” W. In fact, if you were to copy and paste that coordinate in the browser version of Google Earth, you would fly directly to Half Dome. Go ahead and give it a try now!