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Decimal degrees (DD) is a notation for expressing latitude and longitude geographic coordinates as decimal fractions of a degree.DD are used in many geographic information systems (GIS), web mapping applications such as OpenStreetMap, and GPS devices.
The lines from pole to pole are lines of constant longitude, or meridians. The circles parallel to the Equator are circles of constant latitude, or parallels. The graticule shows the latitude and longitude of points on the surface. In this example, meridians are spaced at 6° intervals and parallels at 4° intervals.
Thus longitude at sea could only be estimated from dead reckoning (DR) – by using estimations of speed and course from a known starting position – at a time when longitude determination on land was becoming increasingly accurate. To compensate for longitude uncertainty, navigators have sometimes relied on their accurate knowledge of latitude.
Informally, specifying a geographic location usually means giving the location's latitude and longitude. The numerical values for latitude and longitude can occur in a number of different units or formats: [2] sexagesimal degree: degrees, minutes, and seconds : 40° 26′ 46″ N 79° 58′ 56″ W
A geographic coordinate system (GCS) is a spherical or geodetic coordinate system for measuring and communicating positions directly on Earth as latitude and longitude. [1] It is the simplest, oldest and most widely used type of the various spatial reference systems that are in use, and forms the basis for most others.
The graticule shows the latitude and longitude of points on the surface. In this example meridians are spaced at 6° intervals and parallels at 4° intervals. In geography, latitude is a coordinate that specifies the north–south position of a point on the surface of the Earth or another celestial body.
It is impossible to determine longitude with an accuracy better than 10 nautical miles (19 km) by means of a noon sight without averaging techniques. A noon sight is called a Meridian Altitude. [2] While it is very easy to determine the observer's latitude at noon without knowing the exact time, longitude cannot accurately be measured at noon.
You can also calculate the kilometers per degree of longitude, k, using one of the following formulas (θ is the latitude, 6378.14 km is the equatorial radius, and 6356.8 km is the polar radius): Accurate, assuming a spheroid: