Map schematic layers in HEC-ResSim are like separate transparencies of map components, such as rivers, subbasins, stream gage locations, etc., laid one on top of the other. All map schematic elements (e.g., common computation points, stream alignment) and imported map layers (e.g., shapefiles, .shp) available for display in the map schematic display area (Figure 2.19) are listed in the *Layer Selector (Figure 2.25). Note that the list of layers will change depending on the selected module (e.g., Water Quality module) and module data (e.g., GeometryData1, Geometry dataset in Figure 2.25). For example, from the Watershed Setup module, Study layers are listed that include water quality Stations. However, from the Water Quality module the Study layers are not listed; however, water quality component layers (for selected module data) are present (i.e., Observed Data, Met Data, Geometry, Mass Injection, HEC-RAS imported Cross Sections, and ResSim). The concept of layers in HEC-ResSim is explained in detail in Chapter 4 of the HEC-ResSim User's Manual.