# How to Understand Latitude and Longitude

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A globe is a model of the earth. Globes have horizontal and vertical lines that make up a coordinate grid system. The horizontal lines that cross the earth are the lines of latitude. The vertical lines that cross the earth are the lines of longitude. Each latitude and longitude line has a number. This numbered grid system enables different geographical places around the world to be located easily.

Think of the lines of latitude as parallels of latitude that encircle the earth, with each latitude line being parallel to the equator. The longest line of latitude is the equator and because of this, the equator is 0 degrees. All lines of latitude measure either north or south from the 0-degree line of latitude (the equator). Each latitude line that runs parallel to the equator (either north or south of the equator) has a degree number assigned to it. The first line north of the equator is +15 degrees north. The first line south of the equator is -15 degrees south. As the latitude lines get further away (both north and south) from the equator, the degree numbers get bigger until the final northern latitude line of +90 (the North Pole) and the final southern latitude line of -90 (the South Pole).

Understand that the lines of longitude are vertical lines that encircle the earth with each longitude line being parallel to the Prime Meridian. The Prime Meridian is a vertical line running from the North Pole to the South Pole that crosses over Greenwich, England. The lines of longitude measure either east or west from the 0-degree line of longitude (the Prime Meridian). The first line west of the Prime Meridian is -15 degrees west. The first line east of the Prime Meridian is +15 degrees east. As the longitude lines get further away (both east and west) from the Prime Meridian, the degrees numbers get bigger until reaching the International Date Line (180 degrees both east and west of the Prime Meridian).

Use the lines of latitude and longitude to locate geographical locations on the earth. Describe a specific location by labeling it with the latitude and longitude lines that intersect at that point.

For example, 45.4 degrees latitude north, 75.7 degrees longitude west are the coordinates for Ottawa, Canada. Visit itouchmap.com (see the Resources section for a link) for a latitude and longitude locator that allows you to either enter coordinates and receive the geographical location, or enter a geographical location and receive the coordinates.

#### Tips

• Lines of longitude are also called “meridians.”

The International Date Line is 180 degrees east and west of the Prime Meridian. This means it is an equal distance away both east and west of the Prime Meridian and is halfway around the earth from the Prime Meridian.