How to Read a World Map Grid
To make map reading and geographical positioning easier, world maps include a grid of imaginary lines superimposed over map images. These lines include horizontal "latitude" lines to measure distances north and south of the equator and "longitude" lines to measure distances east and west of the Prime Meridian. When these two numbers are combined, the data point identifies a unique spot on the world map.
Both latitude and longitude are measured in degrees, minutes and seconds, and learning how to use the system is a valuable skill for reading geographical information.
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Things You'll Need
- World map with latitude and longitude lines
- Computer map application (optional)
Instructions
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Locate the closest latitude (horizontal) line to a desired point. In the case of locations in the Southern Hemisphere, choose the closest line north of the point and select the closest line to the south of the point for locations in the Northern Hemisphere.
Latitude lines run parallel to the equator, an imaginary line that runs along the circumference earth and is the same distance from each of the poles. After choosing the closest latitude line, look closer to find secondary lines that will indicate more exact degrees (or minutes or seconds).
The imaginary line grid is based on a spherical model of the Earth. Thus, the sphere is divided into 360 degrees and each degree is further divided into 60 minutes. Each minute, in turn, can be further divided into seconds, although coordinates are often stated as decimal degrees rather than units of degrees, minutes and seconds. Nonetheless, because the Earth is, in fact, not a perfect sphere, the distances between these lines in real space can vary depending on the position of the point on the Earth.
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Locate the closest longitude (vertical) line to a desired point. In the case of locations in the Eastern Hemisphere, choose the closest line west of the point and select the closest line to the east of the point for locations in the Western Hemisphere.
Longitude lines are east and west of the Prime Meridian, an imaginary line that cuts the globe in half vertically through Greenwich, England. Longitude lines determine how far east or west a point is from the Prime Meridian. After choosing the closest longitude line, as with latitude values, look closer to find secondary lines that will indicate additional degrees (or minutes or seconds to be increasingly exact) east or west of the Prime Meridian.
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Combine the two values to create a geographical data point. Any point on the world map will be a certain number of degrees, minutes and seconds north or south latitude from the equator and a certain number of degrees east or west longitude from the Prime Meridian.
New York City, for instance, is at 40 degrees and 47 minutes north latitude and 73 degrees and 58 minutes west longitude, which is to say that the city is about 40 degrees north of the equator and 73 degrees west of the Prime Meridian.
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Tips & Warnings
Remember that the map grid is made up of imaginary lines and that none of these lines actually exists. The system is intended to help map readers designate exact locations on the map by dividing the world into regular sections.
Be sure to remember what hemisphere you're working with and keep directions (north-south and east-west) consistent to correctly read the grid and designate points.
References
Resources
- Photo Credit poster with world map image by Attila Toro from Fotolia.com
