Basic Map Reading (Latitude – Longitude)

definition-of-latitude-longitude
Image globes: geographyworldonline.com

Latitude and Longitude are at the core of map reading, in that they are the imaginary lines which lay on the surface of the earth to form a matrix of coordinates.

Here is a basic explanation, and an easy way to remember which is which…

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LATITUDE

how-to-remember-latitude
Image globes: geographyworldonline.com

Latitude lines are imaginary lines on the earth’s surface. They run east and west around the globe and tell you your distance north or south of the Equator.

Lines of Latitude run parallel to the equator (east-west).

Remember LATITUDE by thinking of a LADDER (sounds similar).

The ladder has rungs which you climb to go up and down, similar to the lines of Latitude which go up and down across the circumference of the globe.

Latitude lines run east and west, but they tell how far up you can go (North) or how far down you can go (South).

The equator is Zero degrees.

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LONGITUDE

how-to-remember-longitude
Image globes: geographyworldonline.com

Lines of Longitude run from pole to pole (north-south) all the way around the globe and tell you your distance east or west from the ‘Prime Meridian’.

The Prime Meridian is Longitude Zero, and is a reference line from which longitude east and west are measured. It passes through Greenwich, England, the site of the Royal Greenwich Observatory.

Remember LONGITUDE by thinking of long, tall telephone poles (because Longitude lines run from pole to pole).

 
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THE MATRIX

Lines of Latitude and Longitude come together to form a matrix/grid.

Latitude and Longitude is the most common grid system used for navigation. It will allow you to pinpoint your location with a high degree of accuracy.

Latitude is angular distance measured north and south of the Equator.

The Equator is 0 degrees.

As you go north of the equator the Latitude increases all the way up to 90 degrees at the north pole.

If you go south of the equator, the Latitude increases all the way up to 90 degrees at the south pole.

In the northern hemisphere the Latitude is always given in degrees North, and in the southern hemisphere it is given in degrees South.

 
Longitude works the same way. It is angular distance measured east and west of the Prime Meridian.

The prime meridian is 0 degrees Longitude.

As you go east from the prime meridian, the Longitude increases to 180 degrees.

As you go west from the prime meridian Longitude increases to 180 degrees.

In the eastern hemisphere the Longitude is given in degrees East, and in the western hemisphere it is given in degrees West.

 
DISTANCES
At the equator, one degree of Latitude or Longitude represents approximately 70 statute miles.

At higher Latitudes the distance of one degree of Longitude decreases, because they all come closer together as they approach the north and south poles (see the images above for visualization).

Latitude however stays the same because they are always equally spaced apart.

Degrees are not accurate enough to find a precise location. At best, one degree of latitude and longitude would define a 70 square mile area.

 
To overcome this problem, 1 degree is divided further into 60′(minutes).

So if 1 degree equals 70 miles, and one degree can be divided into 60′ (minutes), then 1′ (minute) equals 1.2 miles.

Dividing 1 degree into 60′ (minutes) allows one to calculate their position with much better accuracy.

 
In some instances even more accuracy is needed… To do this we can divide 1′ (minute) into 60″(seconds).

If 1′ (minute) equals 1.2 miles, and we can divide it into 60″ (seconds), then 1″ (second) equals 0.02 miles.

 
It is worth taking a few seconds to memorize the following numbers. It will help you to use latitude and longitude more effectively:

   

1 degree = 70 miles
1′ = 1.2 miles
1″ = .02 miles

united-states-latitude-longitude

Example:
Los Angeles
34° 3′ 8″ N / 118° 14′ 34″ W
34 degrees 3 minutes 8 seconds North / 118 degrees 14 minutes 34 seconds West

The map shown above only shows the major degrees. However as you can see, even the coordinates 34° N / 118° W will enable you to sight fairly quickly on the map where Los Angeles is located. If we had a map which indicated ‘minutes’, then you could distinguish down to approximately a mile. If the map indicated “seconds”, then you could pinpoint the exact center down to approximately 100 feet. Think of it as grids within grids… It’s just a matter of having the right map which overlays latitude and longitude down to the resolution that resolves for your purpose.

 
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25 Comments

  1. Doug 09/11/2013
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