Georeferencing is the process by which real-world coordinates are assigned to an HEC-RAS model to reference it to other data. An HEC-RAS model that shares a common coordinate system with GIS layers allows the developer of the model to visualize limits of the defined study area using background data.
The use of aerial photographs, for example, can be extremely beneficial for identifying the location of a landform such as levee or road or structures such as bridges and weirs while showing the user it's representation in the hydraulic model. Therefore, background data is quite useful for model development. HEC-RAS results may also be quickly visualized using automated GIS procedures using tools such as HEC-RAS Mapper and HEC-GeoRAS. Additionally, floodplain maps may also be developed if the HEC-RAS model is georeferenced.
HEC-RAS allows the user to have a stream system schematic, and hydraulic elements, that is drawn spatially correct. This requires that the stream centerlines, cross sections, storage areas, and 2D Flow Areas have GIS coordinate information in order to draw them in a georeferenced framework. Generally, GIS coordinate information can be developed by laying out the model geospatially using HEC-RAS Mapper. However, HEC-RAS also has editors and tools for allowing the user to enter and manipulate GIS coordinate information directly in the HEC-RAS Geometric Data editor. The following is a list of the GIS tools available from the GIS Tools menu at the top of the Geometric Data editor.