CWMS performs an "on-the-fly" coordinate system transformation, allowing the CAVI to display map layers that were created in different coordinate systems in a unified view. For example, you can display your watershed with background maps from Internet sources (Google® Maps, Open Street Map, etc.), and this feature only works correctly if you define a georeferenced coordinate system for the watershed and include a coordinate system definition (*.prj file or equivalent) for each map layer included in the watershed. The positions of elements in the watershed's primary layers (time series icons, stream alignment, and study layers) are stored in the watershed coordinate system. You set the watershed's coordinate system when creating a new watershed. This superimposes a grid on layer features to establish x- and y- coordinates in the World Coordinate System (WCS) for each point on the layer. The x-coordinate is referred to as "easting" and the y-coordinate is referred to as "northing" following customary use in surveying and mapping.
You may need to use GIS tools to identify or transform the layers from one coordinate system to another before using them with CWMS. Although CWMS has the ability to project different coordinate systems "on-the-fly", using a consistent coordinate system may produce more accurate placement of map elements and may result in better performance in displaying large maps.