Pituuskoordinaatti

Pituuskoordinaatti, or longitude coordinate in English, is a geographical coordinate that specifies the east–west position of a point on the Earth's surface. The value is measured along a parallel of latitude, expressed in degrees, minutes, and seconds (DMS) or in decimal degrees (DD). The prime meridian, which runs through Greenwich, England, is defined as 0° longitude; longitudes east of Greenwich are positive up to +180°, while those west are negative up to –180°. In everyday use, directions east or west are often appended to the numeric value rather than using negative numbers, e.g., 75° W instead of –75°.

In modern navigation and mapping systems, pituuskoordinaatit are part of the geographic coordinate system that couples longitude with latitude to locate any point on Earth. The most widely used system is the World Geodetic System 1984 (WGS 84), which underlies GPS receivers and most global positioning databases. When longitude is presented in decimal form, it is usually rounded to a precision that suits the application: for general navigation a precision of ±0.1 km requires about five decimal places (0.00001°), while high‑precision surveying may use seven or more.

Computationally, converting between DMS and DD or converting between linear distances and angular measures requires knowledge of the Earth's ellipsoidal shape. Practical applications range from simple map reading to complex GIS analyses, weather forecasting, satellite communication and global maritime navigation. Thus the pituuskoordinaatti is a fundamental element of spatial data representation and geographic information science.