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Changing Latitude & Longitude to Distance Units
To estimate the difference between stations within a transect, you must convert latitude to miles or kilometers. A one minute change in latitude (north/south distance) is equal to one nautical mile (1.85 km), or 6076 feet (1852 m). There are 60 minutes to one degree, therefore there are 364,560 feet (111,120 m) to one degree change of latitude, or about 69.1 miles (111.3) km). To determine the distance between stations use minutes and a fraction of a minute and then convert to feet or meters. Remember that one degree of latitude has 60 minutes and each minute has 60 seconds.
Example of distance with a change in latitude:
Find the distance between stations E1 (28E 58.0' N) and E2 (28E 51.5' N) at longitude 91E15.0'W.
- Determine the distance between the stations in minutes and a fraction of a minute.
58.0 min - 51.5 min = 6.5 min- Determine number of miles per minute.
69.1 mile/60 min = 1.1517 mile/min (111.3 km/60 min = 1.85 km/min)- Multiply distance by miles per minute.
6.5 min x 1.1517 mile/min = 7.48 mile (6.5 min x 1.85 km/min = 12.02 km)Several transects (D, E, F, G, H, I, J, K) are parallel. You can determine this distance by using the difference in longitude. A one minute of change in longitude (east/west distance) varies with the distance north or south of the equator. The further away from the equator, the smaller the east?west distance associated with a change in longitude. Therefore, for each minute of change in longitude, the distance is different. In Louisiana a one degree difference varies from 60.2 miles (96.9 km) at latitude 29E30' to 60.8 miles (97.8 km) at 28E30'. For the purposes of estimating distances in the Louisiana offshore, use an average one minute change in longitude of about 60.5 miles (97.4 km).
Example of distance with a change in longitude:
Find the distance between transects E (91E15.0'W) and F (91E37.0'W).
- Determine the distance between transects in minutes and seconds.
7.0 min -15.0 min = 22 min- Determine number of miles per minute.
60.5 mile/60 min = 1.0083 mile/min (96.4 km/60min = 1.60 km/min)- Multiply distance by miles per minute.
22.0 min x 1.0083 mi/min = 22.18 mi (22.0 min x 1.6 km/min = 35.2 km)For more accurate distances between stations, a conversion is available at http://jan.ucc.nau.edu/~cvm/latlongdist.php.
