Defining a shapefile's coordinate system by specifying a new geographic coordinate system

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 New and click Geographic.
5. Type a name for the new geographic coordinate system.
6. Type the appropriate semimajor and semiminor or inverse flattening values and type a name for your custom spheroid and datum.

   Alternatively, click the Datum or Spheroid drop-down arrow and click a predefined datum or spheroid.

   Note:

   When creating a custom coordinate system, if you choose an object, such as a datum or spheroid, from one of the drop-down lists, those parameter values will be read-only. To modify them, click the drop-down arrow again and click <custom>. Change the default values appropriately and type a name for your custom set of parameters.
7. Type the appropriate radians per unit and type a name for your custom units.

   Alternatively, click the Angular Unit drop-down arrow and click a predefined unit of measure.

8. Type the appropriate degrees, minutes, and seconds defining the prime meridian and type a name for this line of longitude.

   Alternatively, click the Prime Meridian drop-down arrow and click a predefined line of longitude.

9. Click OK.
10. Click OK on the Shapefile Properties dialog box.