decimalLongitude

decimalLongitude is a geographic coordinate that represents a location’s east–west position on the Earth using decimal degrees. It is typically paired with decimalLatitude to define a point on a map or in a dataset. In most conventions, positive values indicate east of the Prime Meridian and negative values indicate west, with zero at the Greenwich meridian. The common valid range is -180.0 to 180.0 degrees, though some systems may normalize or wrap values differently.

As a numeric value, decimalLongitude is usually stored as a floating-point number. Data precision can vary by source and format, from a few decimal places to many, enabling different levels of positional accuracy. Floating-point representation can introduce minor rounding errors, especially when performing calculations or transforming coordinate reference systems. Decimal longitude is almost always used together with decimal latitude to specify a precise location.

Typical usage includes geographic information systems (GIS), mapping applications, geocoding results, and data exchange formats. Some formats, such as GeoJSON, represent coordinates as [longitude, latitude], making decimalLongitude the first element in the pair. Others may store longitude in separate fields named decimalLongitude and decimalLatitude, depending on the schema.

Examples: a point in San Francisco has a decimalLongitude of -122.4194 and a decimalLatitude of 37.7749. A location in London has a decimalLongitude of -0.1278 and a decimalLatitude of 51.5074.