COORDINATE SYSTEMS AND MAP PROJECTIONS

COORDINATE SYSTEMS Coordinate systems are used for georeferencing used in precise positioning, navigation, and geographic information systems for the location of points in space. There are two types of coordinate systems: Geographic Projected

CARTESIAN COORDINATE SYSTEM A point described by Two-Dimensional Cartesian Coordinates A point described by Three- Dimensional Cartesian Coordinates

GEOGRAPHIC COORDINATE SYSTEMS A geographic coordinate system uses a three dimensional spherical surface to define locations on the earth The most commonly used coordinate system is the latitude, longitude, and height system.

GEOGRAPHIC COORDINATE SYSTEMS Points on the earth are referenced by longitude and latitude to define the location on the surface Longitude and latitude are angles measured from the earth’s center to a point on the earth’s surface.

LATITUDE AND LONGITUDE Latitude and longitude values are measured either in decimal degrees or in degrees, minutes, and seconds (DMS) decimal degrees (DD): -32.5 degrees/minutes/seconds (DMS): 32° 30’ 00” S

Latitude values are measured relative to the equator range from -90° at the South Pole to +90° at the North Pole. Longitude values are measured relative to the prime meridian range from -180° when traveling west to 180° when traveling east. 7

LATITUDE AND LONGITUDE Not uniform units of measure Meridians converge at the Poles 1° longitude at Equator = 111 km at 60° lat. = 55.8 km at 90° lat. = 0 km

HEIGHT Topography - The surface of the Earth. Ellipsoid - GPS heights are referenced to this mathematical surface (e.g.: WGS84) Geoid - The natural surface extension of mean sea level. Source: JUPEM

PROJECTED COORDINATE SYSTEMS A map projection is the systematic transformation of locations on the earth (latitude/longitude) to planar coordinates The basis for this transformation is the geographic coordinate system (which references a datum) Map projections are designed for specific purposes

MAP PROJECTION “A map projection is any method of representing the surface of a sphere or other three-dimensional body on a plane” (from Wikipedia) The earth is roughly spherical and it is necessary to use mathematical methods to portray all of it or portions of it on flat media, i.e. charts. These mathematical methods are call "projections"

MAP PROJECTION A map projection is used to portray all or part of the round Earth on a flat surface. This cannot be done without some distortion. Every projection has its own set of advantages and disadvantages. There is no "best" projection.

CLASSIFICATION OF MAP PROJECTIONS Conformal – local shapes are preserved Equal-Area – areas are preserved Equidistant – distance from a single location to all other locations are preserved Azimuthal – directions from a single location to all other locations are preserved Note: it is impossible to construct a map projection that is both equal-area and conformal

CONFORMAL PROJECTIONS Example: Mercator Common map projection used for nautical purposes because of its ability to represent lines of constant course. Distorts the size and shape of large objects, as the scale increases from the Equator to the poles.

EQUAL-AREA PROJECTIONS Example: Sinusoidal Used for maps of Africa, South America, and other large areas that are mainly north-south in extent. Distances are correct along all parallels and the central meridian(s). Shapes are increasingly distorted away from the central meridian(s) and near the poles.

EQUIDISTANT PROJECTION Example: Plate Carrée The projection is neither equal area nor conformal. Mainly used for thematic mapping A de facto standard for global raster datasets because of the simple relationship between the position of an image pixel on the map and its corresponding geographic location on Earth

UNIVERSE TRANSVERSE MERCATOR PROJECTION (UTM) 2-dimensional Cartesian coordinate system Conformal projection (shapes are preserved) Zones are 6 degrees of longitude wide Minimum scale distortion within zones