Geographic Reference for Map Layers

To maintain a geographic reference (georeference), CWMS uses a user-selected and customizable coordinate system, called the World Coordinate System (WCS). This superimposes a grid on layer features to establish x and y coordinates in WCS for each point on the layer. The x-coordinate is referred to as "easting", and the y-coordinate is referred to as "northing". You can select the extent of this grid, the dimensions of the cells of the grid, the units of measurement of the grid, and the location of the origin of the grid. Because of this flexibility, you can specify and use virtually any grid coordinates convenient for CWMS model integration.

From the CWMS CAVI main window, under the Maps menu, click Default Map Properties. The Default Map Properties dialog will open. The Default Map Properties dialog contains two tabs: Map Extents and Default Map Layers.

The Map Extents tab includes: 

• Coordinate System - This field identifies the established coordinate system for the watershed. To view the coordinate system, from the Default Map Properties dialog, click View. The Map Coordinate Information dialog will open, providing you with information about the coordinate system that was established when the watershed was created. You are not able to edit this information.
  
• Extents - Easting Minimum and Maximum; Northing Minimum and Maximum. These values indicate the location of the left, right, bottom and top borders (respectively) of the grid in the map window. 
• Set Map Extents to Display - This will set the limits of the map window. If you zoom in on an area and click Set Map to Extents to Display, the extents on the Default Map Properties dialog will change to the zoomed area.
• Grow to Map Extents - When selected, the CWMS software automatically sets the geographic extents to the smallest rectangle that encompasses all the objects in the watershed.

The geographic extents of map layers must be selected carefully to ensure that the entire watershed is included. CWMS can transform map layer coordinates "on-the-fly" if coordinate systems are defined properly. For example, an ArcGIS shapefile has an associated projection (.prj) file. The projection file contains the mathematical formulas to relate spherical coordinates on the globe to flat, planar coordinates. 

The Default Map Layers tab includes a list of map layers that are being displayed in a map window. You can display or hide map layers by checking or unchecking the boxes next to the layers.