Longitude and latitude form a standardized global grid system for precisely identifying any location on Earth. Coordinates are expressed as angular measurements relative to two fixed reference lines: the Equator (for latitude) and the Prime Meridian (for longitude). Latitude measures distance north or south (0° to 90°), while longitude measures distance east or west (0° to 180°). Because various fields require different levels of precision, three internationally recognized formats exist for writing these coordinates. This guide explains the structure and mandatory rules for their correct notation.
The Three Standard Coordinate Formats
The most common method is Decimal Degrees (DD), which expresses both latitude and longitude as simple decimal numbers. The whole degree measurement and the fractional part are combined into a single value, such as 40.7128°. This structure is the simplest for computer processing and is widely used in Geographical Information Systems (GIS) and online mapping services.
A second, more traditional format is Degrees Minutes Seconds (DMS). This format breaks down each degree into smaller units: 60 minutes (‘) per degree, and 60 seconds (“) per minute. A coordinate appears as 40° 42′ 46” N, providing high precision for traditional surveying and printed maps.
The third standard is Degrees Decimal Minutes (DDM), a hybrid format. It uses degrees and minutes, but the seconds component is converted into a decimal fraction of the minute (e.g., 40° 42.7667’ N). DDM is preferred in maritime and aviation navigation, balancing human readability and precision. It is often easier for electronic navigation equipment to display than the full DMS format.
Essential Rules for Proper Notation
The latitude value must always precede the longitude value in the pair (Lat, Lon). This standard order is a non-negotiable convention. This sequence ensures the location is correctly plotted, whether written on a map or entered into a system.
Coordinates indicate the hemisphere using either directional letters or a sign convention. The letter method uses a cardinal direction letter following the numerical value: North (N) or South (S) for latitude, and East (E) or West (W) for longitude (e.g., 40° N, 74° W).
The sign convention uses positive and negative values to define the hemisphere, eliminating letters. North latitude and East longitude are positive; South latitude and West longitude are negative. Thus, 40° N, 74° W becomes 40, -74 (the positive sign is often omitted). Do not mix these two methods; a coordinate should not use both a negative sign and a directional letter.
The latitude and longitude values must be separated clearly. In formal notation, a comma or a space distinguishes the two values. For Decimal Degrees, the pair is almost universally separated by a comma (e.g., 40.7128, -74.0060).
Entering Coordinates into Digital Platforms
Digital platforms, including mapping services and GPS devices, prioritize machine processing. Most modern systems prefer the Decimal Degrees (DD) format due to its clean, numerical structure. Fractional degrees are computationally efficient, allowing software to easily store and manipulate the data.
When entering coordinates, the sign convention is almost always mandatory, replacing directional letters. A negative sign unambiguously indicates the Southern and Western hemispheres. The required digital format is the Latitude value, followed by a comma, and then the Longitude value (e.g., 34.0522, -118.2437).
While some digital tools convert DMS, relying on Decimal Degrees with the sign convention minimizes ambiguity and ensures correct interpretation. The system requires the correct Lat/Lon order and proper sign to prevent plotting the location in the wrong hemisphere.