GPS coordinates provide a unique numerical address for any location on Earth, allowing for precise navigation and mapping. These coordinates are derived from the Global Positioning System (GPS), a network of satellites that transmit signals to receivers on the ground. Understanding how to correctly write and interpret these coordinates is necessary for anyone using modern navigation tools. The correct format ensures the intended location is accurately communicated across different devices and systems.
Understanding Latitude and Longitude
A geographic location is defined by two angular measurements: latitude and longitude, which together form a coordinate pair. Latitude specifies the north-south position of a point relative to the Equator, which is the zero-degree reference line circling the Earth’s middle. Lines of latitude, known as parallels, run horizontally and are measured from 0° at the Equator up to 90° at the North and South Poles.
Longitude specifies the east-west position relative to the Prime Meridian, which is the zero-degree reference line that passes through Greenwich, England. Lines of longitude, called meridians, run vertically from pole to pole and are measured from 0° at the Prime Meridian up to 180° east or west. A complete coordinate requires both a latitude and a longitude value to pinpoint a single spot on the planet’s surface.
The Three Standard Writing Formats
GPS coordinates are commonly expressed in one of three standard formats, each using a different method to represent the fractional part of a degree. The traditional method is Degrees, Minutes, Seconds (DMS), which divides each degree into 60 minutes and each minute into 60 seconds. This format uses the symbols for degrees (°), minutes (‘), and seconds (“)—for example, 40° 42′ 46″ N, 74° 00′ 21” W.
The second format is Degrees and Decimal Minutes (DDM), a hybrid approach frequently used in marine and aviation navigation. This format keeps the whole degrees but expresses the minutes as a decimal number, eliminating the seconds component. A coordinate in this style would look like 40° 42.767′ N, 74° 00.350’ W.
The third format is Decimal Degrees (DD), which is widely used in computer-based mapping systems and modern GPS devices. This format expresses the entire coordinate as a single number with a decimal fraction, removing both minutes and seconds. The same location would be written as 40.7127° N, 74.0058° W.
Using Hemisphere Indicators Correctly
To ensure a coordinate is unambiguous, a hemisphere indicator must be included to specify the direction from the zero-degree reference lines. There are two methods for indicating direction: alphanumeric and signed notation. The alphanumeric method uses letters to denote the hemisphere, such as N (North) or S (South) for latitude, and E (East) or W (West) for longitude.
When using the DMS or DDM formats, the alphanumeric indicator is typically placed immediately after the numerical value, such as 34° 03′ 12″ S. The signed notation method, most common with Decimal Degrees, uses positive and negative signs instead of letters. North latitude and East longitude are positive values, while South latitude and West longitude are negative values. For example, a location in the Southern and Western hemispheres would be written as -34.0533, -118.2428.
Practical Tips and Common Errors
A fundamental rule for writing GPS coordinates is to always list the latitude value first, followed by the longitude value (Lat/Lon). This order is a universal standard, and reversing it will point to an entirely different location. The two values should be separated by a comma or a space, though a comma is the most widely accepted separator, especially in the Decimal Degrees format.
The number of decimal places used directly relates to the precision of the location, with more digits indicating greater accuracy. For instance, using four decimal places in Decimal Degrees provides accuracy to within about 10 meters, which is sufficient for most consumer applications. A frequent mistake is forgetting to include the hemisphere indicator (the N/S/E/W letter or the negative sign for South and West), which makes the coordinate ambiguous.