![]() This procedure is necessary for using many of the geoprocessing tools, such as those relating to distance or nearness analysis. It creates a new, projected, layer (doesn't alter the original). Project: This tool allows you to change the projection of a layer, or to project an unprojected layer.You can also define the projection in ArcCatalog. Define Projection: This tool allows you to tell ArcGIS what projection/coordiates/datum a layer is using, if such information wasn't included with the layer (layer Properties shows Unknown projection under Source).Useful discussion of issues surrounding Coordinate Systems and Data Frames. The projection/coordinate system doesn't need to be the same as the layers, as long as everything is defined. To get them to overlay, you must define the unknown layers' projections, then also define the Data Frame's coordinates.įor visualization (doesn't affect the projection of the underlying layers), once everything is defined you can change the look of the map on the fly in the Data Frame properties. Subsequent unprojected lat/long layers will overlay properly, but projected layers won't. If the first layer has undefined geographic (latitude/longitude) coordinates, then ArcGIS discerns degrees and the cursor's position will display as degrees, but the Data Frame properties will still show an unknown coordinate system.If the first layer is undefined (unknown coordinates), then to get layers in other projections to overlay, in addition to using Define Projection on it and any other undefined layer, you'll need to change the Data Frame's coordinate system in the dialog. ![]()
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