Earth scientists determine positions on earth by the angular measurements of latitude and longitude. The earth has a fixed circumference, so you can convert these to feet by calculating the distance the angles defined by latitude and longitude sweep. Angular measurements range range from -180 degrees and 180 degrees with respect to a reference, which is the equator when measuring latitude and the prime meridian when measuring longitude. You'll need your calculator to convert these angles to distances from their respected references.
Convert the latitude and longitude measurements from degrees, minutes and seconds to decimal notation. The conversion factors are 60 seconds per minute and 60 minutes per degree. This example is for Denver International Airport.
Lon: -104° 40’ 23”. 23 seconds is 23/60 = .383 minutes. 40.383 minutes is 40.383/60 = 0.673 degrees, so the longitude equals 104.673˚. We can convert the latitude in a similar way: Lat : 39° 51’ 42” = 39° 51.7’ = 39.862°.
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Convert the decimal degrees to km. The circumference of the earth around the equator is slightly different of that around the poles, because the planet isn't perfectly round. However, they differ by only 42 km., and are both approximately 40,000 km. This makes the conversion factor 10,000km per 90 degrees. This factor is easier to remember and easier to use than converting directly to feet.
Longitude: -104.673 * (10,000/90) = -11,630.34km. This is the distance of DIA from the prime meridian.
Latitude: 39.8617 * (10,000/90) = 4429.1km. This is the distance of DIA from the equator.
Convert kilometers to feet using the conversion factor 3280.4 feet per kilometer.
-11,630.34 * 3280.4 = - 3.815 x 107 feet
4429.1 * 3280.34 = 1.453 x 107 feet
The negative sign in front of the longitude value indicates the distance is west of the prime meridian.
This calculation gives the position of Denver International Airport as 38.15 million feet west of the prime meridian and 14.53 million feet north of the equator.