Latitude and Longitude are measurements used to identify and locate specific places on earth. Every location on the globe has a unique latitude and longitude. Latitude is defined as the distance of a point north or south of the equator. Lines of latitude are parallel to the equator and are often referred to as parallels. Longitude is defined as the distance of a point east or west of the Prime Meridian. Lines of latitude are often called meridians.

A line to the east of the Prime Meridian has a positive value and a line to the west has a negative value. Think of it as a scale with the zero value in the middle. The same thing applies to latitude. Any line north of the equator is a positive value and any line south is a negative value.

Both latitude and longitude lines are measured in degrees, minutes and seconds. But these are not the minutes and seconds we know as time. Think of minutes and second simply as units of measurement. There are 60 minutes in 1 degree, and 60 seconds in 1 minute. The measurements in minutes and seconds are used to identify the precise location of a point on the map. For example, a latitude of 75 degrees, 35 minutes, 15 seconds (written as 75:35:15) means that we are near the 75 degree point north of the equator (because the value is positive). Because there are 60 minutes in 1 degree, a measurement of 35 minutes means that we are a little more than half way between 75 and 76 degrees. Once we find the 35 minute mark, we get even more accurate using seconds. There are 60 seconds in minute, therefore 15 seconds is one quarter of a minute. We can divide a minute into four equal parts and the first of the pars will be our 15 second mark.

Let's try determining latitude and longitude using the map above. If at any time you would like to see a large picture of the map, just click on it.

Lets find the latitude and longitude of the red star. Along the edge of the map there are measurements of latitude and longitude. They were derived from the measurements at the top left corner. Remember, latitude always measures east to west and longitude always measures north to south.

The latitude of the red star is 40 degrees, 51 minutes. We determine this by lining the star up with the closest latitude measurement. In this case the star lines up directly with 40 degrees, 51 minutes. The longitude of the red star is measured at the midpoint between 75 degrees, 35 minutes and 75 degrees 36 minutes. In this case we read the longitude at 75 degrees, 35 minutes and 30 seconds. The 30 second measurement is used because the star is aligned at the midpoint between the two minutes and half of one minute is 30 seconds. We could break the minute down further, if it were necessary.