For example, a stream in a large-scale map may appear to flow in a different direction using an ellipsoidal vertical coordinate system. Since they are calculated on a mathematical model, ellipsoidal coordinate systems are simpler than gravity-based vertical coordinate systems, but they may lack significant accuracy, especially in large-scale applications. They reference a mean sea level calculation (or in some cases, derived from the level of a single point).Įllipsoidal coordinate systems reference a mathematically derived spheroidal or ellipsoidal surface. Gravity-based vertical coordinate systems are more commonly used. Vertical coordinate systems are either gravity based or ellipsoidal. Local coordinate systems are usually expressed in meters or feet. The false origin may or may not be aligned to a known real-world coordinate, but for the purpose of data capture, bearings and distances can be measured using the local coordinate system rather than global coordinates. Local coordinate systems are often used for large-scale (small area) mapping. A map projection contains the mathematical calculations that convert the angular geodetic coordinates of the GCS to Cartesian coordinates of the planar PCS system.ĭownload the list of supported projected coordinate systems.Ī geographic coordinate system (left) measured in angular units is compared to a projected coordinate system (right) measured in linear units for the same location in the Atlantic Ocean.Ī local coordinate system uses a false origin (0, 0 or other values) in an arbitrary location anywhere on earth.

A projected coordinate system is composed of a geographic coordinate system and a map projection together. Projected coordinate systems (PCS) are planar systems that use linear measurements for the coordinates rather than angular units. The location of data is expressed as positive or negative numbers: positive x- and y-values for north of the equator and east of the prime meridian and negative values for south of the equator and west of the prime meridian.ĭownload the list of supported geographic and vertical coordinate systems. Geographic coordinate systems (GCS) are based on a three-dimensional ellipsoidal or spherical surface, and locations are defined using angular measurements, usually in decimal degrees, measuring degrees of longitude (x-coordinates) and degrees of latitude (y-coordinates). You can determine which type of coordinate system your data uses by examining the layer's properties. Horizontal coordinate systems can be of three types: geographic, projected, or local. Horizontal coordinate systems locate data across the surface of the earth, and vertical coordinate systems locate the relative height or depth of data. Coordinate systemsĭata is defined in both horizontal and vertical coordinate systems. Identifying this measurement system is the first step to choosing a coordinate system that displays your data in its correct position in ArcGIS Pro, in relation to your other data. The coordinates can be specified in many ways, such as decimal degrees, feet, meters, or kilometers any form of measurement can be used as a coordinate system. These numbers are part of a coordinate system that provides a frame of reference for your data to locate features on the surface of the earth, to align your data relative to other data, to perform spatially accurate analysis, and to create maps.Īll spatial data is created in a coordinate system, whether it is points, lines, polygons, rasters, or annotation. Spatial data is similar, but it also includes numerical information that allows you to position it on earth.

Data usually comprises an array of numbers.

Emory method map projections