![]() You can see that it references the same DATUM, SPHEROID, PRIMEM and UNIT fields as the 4236 projection expalaind in the GCS section earlier. The following example is the string representation of the California State Plane Zone, which is a projected coordinate system (PCS), with a wkid of 3857. A projected coordinate system consists of a linear unit of measure (usually meters or feet), a map projection, the specific parameters used by the map projection, and a geographic coordinate system. A map projection is designed to minimize the distortion caused by flattening the Earth's surface. Converting from three to two dimensions causes distortions. A map projection is a set of mathematical equations to convert from longitude and latitude (i, j) to planar coordinates (x, y). Three-dimensional geographic data is converted to planar coordinates via a map projection. When your data is in a GCS, ArcGIS can still draw it on a flat surface (such as the map-widget) by projecting to an appropriate PCS on-the-fly for the purpose of display.įurther, many types of analyses and data are designed for two-dimensional or planar coordinates. A projected coordinate system is always based on a geographic coordinate system that references a specific datum. Unlike a geographic coordinate system, a projected coordinate system has constant lengths, angles, and areas across the two dimensions. To draw / display any geographic data on a flat map or surface such as the computer screen, it needs to be in a PCS. Projected Coordinate Systems (PCS) define a flat 2D Cartesian surface. To see the list of supported GCS, their wkt and wkid (explained below), go here. The wkt of a GCS has 3 main parts: a DATUM, SPHEROID and a PRIMEM (prime meridian). Each GCS has a well-known text ( wkt), representing the details and a well-known id ( wkid), 4326 in this example, which is used in developer APIs such as the REST API and in the Python API. The name for this system is GCS_WGS_1984. The following example is a string representing a geographic coordinate system (GCS) based on the WGS 1984 datum. A datum, which is an ellipsoidal (spheroid) model of the EarthĬommon datums include WGS84 (used in GPS) and NAD83 (used in surveying and mapping in North America).There are three parts to a geographic coordinate system: It uses an ellipsoidal surface for approximation and uses angular units to define locations on the Earth. Geographic coordinate systemĪ geographic coordinate system (GCS) treats the Earth as a 3D spherical surface. Thus spatial reference system must be clearly defined not only to verify the integrity of geometric calculations between shapes, but also to allow transformations to take place between shapes in different coordinate systems. To integrate spatial data from various sources, the data must be transformed to a common coordinate system. Most spatial references fall into one of two categories - geographic coordinate systems and projected coordinate systems. When spatial data is created, it is often specified with a spatial reference in the form a particular coordinate system. ArcGIS supports over a thousand such systems, called coordinate systems or coordinate reference systems. These models are a mathematical approximations of Earth and as such, each model is designed to suit a specific purpose - such as for navigation, area calculation, large area display etc. For people that are new to GIS, this may come as a surprise, there are several such models to represent Earth. Spatial reference defines the measurement system used to locate the geometry on a model of the Earth. Before we get any further into these individual geometry types, we need to discuss about an important concept called spatial reference Spatial Reference and Coordinate Systems The geometry module of the ArcGIS API for Python provides a pythonic model to construct, visualize and work with geometries. The topic Features and Geometries provides you more information and examples of geometries and how it relates to the ArcGIS developer ecosystem. Polygons define a closed shape (consisting of a series of polylines), such as the outline of a property parcel, outline of a lake or school campus. Polylines define a series of points representing a line, such as a road or a river or an oil pipeline. ![]() They define a single location, such as the user's GPS coordinates, locations of earthquakes, location of your parked car etc. Points - these are the simplest forms of geometries. In GIS, a geometry could be of the following types: In GIS applications, vector geometry is used to represent the spatial component of geographic features with discrete boundaries such as wells, rivers, states, streets, and parcels. Geometry is the branch of mathematics dealing with spatial relationships, measures, and properties of points, lines, and surfaces.
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