You can watch the video Introducing Coordinate Systems and Map Projections to learn more about all of these terms and concepts. What’s the difference between a spatial reference and a coordinate system? To learn more, read Projection on the fly and geographic transformations. If your data uses a different GCS than your map, and you don’t use a geographic transformation, the data will draw in the wrong place. You can choose which transformation to use. They are sometimes referred to as datum transformations. These are calculations that convert coordinates from one GCS to another. Whenever projection on the fly includes converting between geographic coordinate systems, the process will include geographic transformations. ![]() If you didn’t have projection on-the-fly, you wouldn’t be able to draw the data before first converting it to the same coordinate system as the map. Projection on the fly is what ArcGIS does to resolve conflicts when your data is in a different coordinate system than your map. Geographic transformations are one part of the projection on the fly process. To learn more, see Define Projection or Project? What’s the difference between projection on the fly and geographic transformations? It also updates the metadata information. The Project tool converts all coordinates from one coordinate system to another. It won’t change the actual coordinate values. It reassigns the coordinate system information in the metadata. The Define Projection tool is used mainly when data has an unknown coordinate system. What’s the difference between the Define Projection tool and the Project tool? The authority of the WKID will either be EPSG (European Petroleum Survey Group) or Esri but these numbers don’t overlap, so there’s no need to worry about which authority defined the ID. Its units are linear, most commonly in meters. It contains a GCS, but it converts that GCS into a flat surface, using math (the projection algorithm) and other parameters. Its units are angular, usually degrees.Ī projected coordinate system (PCS) is flat. What’s the difference between a GCS and a PCS?Ī geographic coordinate system (GCS) is a reference framework that defines the locations of features on a model of the earth. A spatial reference and a coordinate system?.Projection on the fly and geographic transformations?. ![]()
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