Latitude and Longitude

Latitude and longitude refers to a system of imaginary east–west and north–south lines. These lines crisscross the Earth. By naming one line of latitude and one line of longitude, one may locate any point on the surface of the Earth.

You would probably have little use for latitude or longitude while trying to find a place in a town or city. You would find it more convenient to use a map that showed local streets and avenues. But you might need latitude and longitude to locate yourself in a place such as an ocean or a desert. At such places, you would not see streets or avenues.


Latitude is a measurement of distance north or south of the equator. The equator is an imaginary east–west line. It circles the Earth halfway between the North and South poles. And it divides the Earth into a Northern Hemisphere and a Southern Hemisphere.

Other imaginary east–west lines circle the Earth. They are parallel to the equator. And they are north and south of it.

Because these lines are parallel to the equator, they are called parallels. Each parallel marks off a fixed distance north or south of the equator. This distance is called latitude. All points in the Northern Hemisphere have north latitude. All points in the Southern Hemisphere have south latitude.

Latitude Units

Latitude is expressed in degrees (°). Each degree is 1/360 of the 360 degrees of a full circle. By definition, latitude is 0° at the equator. The distance from the equator to the North Pole or to the South Pole is one-fourth of a circle around the Earth. And one-fourth of a circle's 360° is equal to 90°. Thus the North Pole has a latitude of 90° N. The South Pole has a latitude of 90° S. These are the highest latitudes north or south of the equator.

A point midway between the equator and the poles has a latitude of 45°. (Depending on the direction from the equator, the point may have a latitude of 45° N or 45° S.) A latitude of 30° is one-third of the way from equator to pole, and so forth.

Latitude and Miles

Even though latitude is always measured and expressed in degrees, it is easily converted into miles. The distance from the equator to either pole is 6,222 statute miles, or standard miles (10,013 kilometers). Divided by 90° from equator to pole, this equals about 69 statute miles (111 kilometers) for each degree of latitude.

The distance per degree of latitude varies slightly from the equator to the poles. It varies because the Earth is not perfectly round. For example, the Earth is flattest at the poles. A degree of latitude is almost a mile longer there than at the equator.

If you know the latitude of a place, you can thus estimate its distance from the equator. For example, Montreal, Canada, is located at about 45° N latitude. By multiplying 45 by 69, you find that Montreal is about 3,105 statute miles north of the equator. Philadelphia, Pennsylvania, is located at about 40° N. Montreal is thus about 345 statute miles farther north than Philadelphia. (One multiplies the 5 degrees difference by 69 miles).

Degrees are too large for determining the precise locations of places. Therefore degrees are subdivided into minutes and seconds. Each degree has 60 minutes (60′). And each minute has 60 seconds (60″). One minute is equal to about 1 1/6 statute miles, or about 6,000 feet. One second is equal to about 100 feet. Latitude may thus be given more precisely in degrees, minutes, and seconds. The latitude of Montreal, for example, is 45° 31′ N.


Latitude by itself tells only how far a place is from the equator. It locates the place somewhere on an east–west parallel thousands of miles long extending around the Earth. It is possible to pinpoint a place on any parallel by using a series of imaginary north–south lines that intersect the parallels at right angles.

The north–south lines that run perpendicular to the parallels are called meridians. Each meridian is a circle that runs north and south around the Earth through the North and South poles. Parallels indicate distances in a north–south direction. Meridians indicate distances in an east–west direction.

With parallels, there is a natural midway line between the North and South poles. This is the equator. With meridians, there is no natural midway line on the Earth from east to west. The world's nations, however, have agreed on a starting line. This is the meridian that runs through Greenwich Observatory near London, England. This meridian is called the prime meridian. Its longitude is 0°. Every other meridian indicates a distance east or west of the prime meridian. This distance is called longitude.

Longitude Units

Longitude, like latitude, is measured in degrees. The half of the Earth east of the prime meridian has longitude up to 180° E. The half west of the prime meridian has longitude up to 180° W. The 180th meridian lies directly opposite the prime meridian. The 180th meridian is the same for both east and west longitude. It is therefore not referred to as 180° E or 180° W, but simply 180°. Midway between the prime meridian and the 180th meridian is 90° W or 90° E, depending on the direction from the prime meridian. One-fourth of the distance is 45°, and so on.

Longitude and Miles

At the equator, 1° of longitude is about the same distance as 1° of latitude. Unlike parallels, however, meridians do not stay the same distance apart at all places on Earth. As meridians move away from the equator they come closer and closer together until they finally meet at the poles. This means that the number of miles in 1° of longitude is different for each latitude. The poles have no longitude because all meridians meet there. Longitude degrees are also subdivided into minutes and seconds to locate places more precisely.

Using Latitude and Longitude

The location of places on the Earth can be pinpointed by using both latitude and longitude. For example, St. Louis, Missouri has a latitude of 39° N and a longitude of 90° W. It is located where the 39° N parallel intersects the 90° W meridian. Places can be located even more precisely by expressing latitude and longitude in degrees, minutes, and seconds.

Samuel N. Namowitz
Earth Science

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SOURCE: The New Book of Knowledge

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