Layers in the CAVI are like transparencies laid one on top of the other. Each layer includes representations of physical images such as roads, county and state boundaries, rivers, and subbasins. These are layered in the map window as color pictures. Each of these images, along with the associated data, is a layer. This chapter describes how you create and manage layers so that required data and information are easily viewed.
There are two types of layers: primary layers and map layers. Primary layers are automatically generated when a new watershed is created and are present in all CWMS watersheds (although some primary layers may be empty in some watersheds) and are module specific. CWMS creates primary layers when a stream alignment, time series icons, map window elements, and gridded precipitation data are created. (A time series icon is a symbol in the map window that provides quick access to time-series data and information that has been assigned to the icon.) CWMS also creates a primary layer when a forecast alternative has been selected for computation. Primary layers can contain sub-layers, for example, the Time Series Icons Layer can have several user-defined sub-layers that represent various types of data and information such as flow and precipitation.
Map layers are optional and are loaded into the watershed by the user. Map layers are physical images, which help visualize a watershed. In CWMS there are several formats for map layers, and include maps from the Internet, such as a Google street map. With the Display Map Coordinates function in the Maps menu, the user can set which coordinates the Map Window will use (watershed or loaded Internet map).