Latitude and Longitude: Difference between revisions

=== History of Formats for Recording and Reporting Latitude and Longitude ===

Recording a location by longitude and latitude has a long history associated with the history of navigating at sea. Traditionally, latitude varies from 0 to 90 degrees north or south with each degree divided into 60 minutes and each minute divided into 60 seconds.  Note that these minutes and and seconds have nothing directly to do with time. Exactly 0 degrees latitude is associated with the equator.  In contrast, longitude varies from 0 to 180 degrees west or east with 0 degrees corresponding to the longitude of Greenwich, England.  As with latitude, each degree of longitude has been traditionally divided into 60 minutes and each minute into 60 seconds. Longitudes east of Greenwich are referred to as east (E) latitudes and those west of Greenwich as west (W). This system is referred to as sexagesimal or DMS format.

Modern nautical charts usually omit seconds and use fractional minutes instead. In place of seconds the minutes part of a latitude or longitude is expressed by adding digits to the right of the decimal point.  For instance, a latitude might be expressed as 45 degrees, 29.32 minutes North. One reason for this convention is that one minute of latitude is almost exactly one nautical mile.

With the advent of computers and GPS satellites, dividing degrees into minutes has become less common. Instead, latitude and longitude are expressed as degrees with many digits after the decimal point, for instance 45.471687 N, 122.728182 W.  Finally, the North (N) or South (S) is often left off the latitude in favor of using positive numbers for latitudes north of the equator and negative numbers for south of the equator.  Similarly, longitudes west of Greenwich are often reported as negative numbers and those east reported as positive numbers. This format where only positive or negative degrees are reported is referred to as '''Decimal Degrees'''. For example, 45.471687, -122.728182.