A vertical coordinate system can be based on a different datum than its horizontal coordinate system counterpart. Some raster data may have a vertical coordinate system (or z-coordinate system) in addition to a horizontal geographic or projected coordinate system. A map projection uses mathematical formulas to relate spherical coordinates on the globe to flat, planar coordinates. A projected coordinate system is defined on a flat, two-dimensional surface, like a printed or displayed map-hence, this is also referred to as a map projection.Latitude and longitude define a global or spherical coordinate system. A geographic coordinate system uses a three-dimensional, spherical surface to define locations on the earth (where coordinates are measured from the earth's center).There are two common types of coordinate systems used in GIS: Other measurement system properties such as a spheroid of reference a datum and projection parameters like one or more standard parallels, a central meridian, and possible shifts in the x and y directions.The definition of the map projection for projected coordinate systems.The unit of measurement (typically feet or meters for projected coordinate systems or decimal degrees for latitude-longitude).Its measurement framework, which is either geographic or planimetric.Each coordinate system is defined by the following: There are many kinds of coordinate systems. Generally, in ArcGIS, when you use a spatial reference system, this encompasses both the geographic and projected coordinate systems. The terms coordinate system and spatial reference system can be used interchangeably. When you define a spatial reference system for a raster catalog or mosaic dataset, you are generally not defining the projection used to store the raster data but the projection that is used to manage the data and create the footprints, boundaries, or other features.Ī spatial reference is the georeferencing and coordinate system assigned to any geographic data, including raster datasets, raster catalogs, and mosaic datasets. This has a direct effect on the cells, as they are permanently resampled to fit this projection. When you define a spatial reference system for a raster dataset, you are defining the projection used to store the data. You want to minimize this to maintain the best image and data quality. This is useful however, each time a raster dataset is transformed, there is a change in the cells as they are resampled. ArcGIS applications, such as ArcMap, or datasets, such as mosaic datasets, can reproject on the fly. Defining the correct spatial reference system for your raster data is important.
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