For convenience in locating the geographic position of different places on the Earth's surface, the surface is covered by an imaginary grid, which is depicted on maps as vertical and horizontal lines. The vertical lines, which join the two poles, are called lines of longitude, and the horizontal lines, which are parallel to the equator, are called lines of latitude. Longitude is split into 360 degrees, 180 degrees to the east and to the west of Greenwich, through which the Zero degree meridian passes. Latitude is split into 180 degrees, 90 degrees north and south of the equator.
Determine the Latitude
In order to calculate the difference in latitude of two places, you first need to know the latitude of each of the two individual locations. There are several ways of determining this. The traditional way is to look up the location on a map that shows latitude and longitude and to measure the latitude using a pair of dividers. The second, and probably the easiest way, is to look it up on an Internet search, and the third is to use a program such as Google Earth, and read it off the screen.
Making the Calculation
Here's where your math is put to test. If both locations are on the same side of the equator, then you must deduct the smaller figure from the larger. If they are on opposite sides of the equator, then you must add the two figures together. Forget about any minus signs that you may see -- they just signify that the figure is the number of degrees to the south of the equator.
As an example you can use Denver, Colorado, and Albuquerque, New Mexico. Looking up Denver will give you 39.74 degrees and Albuquerque will give 35.11 degrees. Take the smaller away from the larger to get the difference, which is 4.74 degrees, the difference in latitude. As another example you can use Denver again and Buenos Aires. Denver, once again is 39.74 degrees and Buenos Aires is -34.61 degrees south of the equator, so add the two figures together, giving a latitude difference of 74.35 degrees.
Converting Latitude Difference to Miles
Since knowing the number of degrees difference may not mean much to many people, you may want to convert the figure into miles. You'll probably need a calculator for this. One degree of latitude is the equivalent of 60 nautical miles, so taking the second example, multiply the difference, 74.35 by 60, giving an answer of 4,461 nautical miles. If you want this answer in everyday American miles you must further multiply by 1.15 since one nautical mile is the equivalent of 1.150782 statute miles. The answer is that Buenos Aires is 5,130 miles to the south of Denver.