Most commonly used CRSs have been assigned a “EPSG code” (EPSG standsįor European Petroleum Survey Group). PROJ.4 is the name of an open source software library that is Trivial to document a projection used, and several systems exist. Number of parameters depends on the projection. The parameters determine things like where the center of the map is. No two dimensional map projection can be both conformal andĮqual-area (but they can be approximately both for smaller areas,Į.g. UTM, or Lambert Equal Area for a larger area), and some areĪ planar CRS is defined by a projection, datum, and a set of parameters. “conformal” (the shapes of the geographic features are as they are seen Whether it is “equal area” (the scale of the map is constant) or One of the most important characteristics of a map projection is Of the whole world other projections are appropriate for small areas ‘Robinson’, ‘Lambert’, ‘Sinusoidal’ ‘Robinson’ and ‘Albers’.
The different types of planar coordinate reference systemsĪre referred to as ‘projections’. A planar system is easier to useįor certain calculations and required to make maps (unless you have aģ-d printer). This three dimensional angular system to a two dimensional planar They are longitude/latitude relative to the WGS84 datum).Ī major question in spatial analysis and cartography is how to transform That is meaningless but they typically mean to say that (Sometimes people say that their coordinates are So the basic way to record a location is a coordinate pair in degreesĪnd a reference datum. Other, local datumsĮxist to more precisely record locations for a single country or region.
Similar to NAD83 (The North American Datum of 1983). Used datum is called WGS84 (World Geodesic System 1984). More complexĭatums allow for more variation in the earth’s shape.
Is ‘flattened’ at the poles and bulges at the equator). The simplest datums are a spheroid (a sphere that To do so, you need a model of the shape of the earth. Obviously we cannot actually measure these angles. (lines of constant longitude) to a meridian that passes through the Longitude (lambda) is the angle from a reference meridian The latitude (phi) of a point is the angle between theĮquatorial plane and the line that passes through a point and the center Reference system for geographic data is longitude/latitude. The earth has an irregular spheroid-like shape.
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