Defining a shapefile's coordinate system by modifying a coordinate system's parameters

Steps:

1. In ArcCatalog, click the shapefile whose coordinate system you want to define.
2. Click the File menu and click Properties.
3. Click the XY Coordinate System tab.
4. Click Modify.

   The Geographic Coordinate System Properties or Projected Coordinate System Properties dialog box appears.

5. Follow the steps for defining either a new geographic coordinate system or a new projected coordinate system to change the appropriate parameters.
6. Click OK.
7. Click OK on the Shapefile Properties dialog box.