Calculating the XY Coordinates of the Centroids of a polygon shapefile

1. Optionally, start an edit session in ArcMap. Calculating a field is faster outside of an edit session, but you won't be able to undo the calculation.
2. Open the attribute table of the layer you want to edit.
3. Right-click the field heading for the X field (if there is no X field you can add a new field by clicking the options button and selecting the new field option).
4. Click Calculate Values.
5. Check Advanced.
6. Type the following VBA statement in the first text box.

   Dim dblX As Double
   Dim pArea As IArea
   Set pArea = [Shape]
   dblX = pArea.Centroid.X

7. Type the variable dblX in the text box directly under the X field name.
8. Click OK.

You can repeat the same process for updating a field with the Y coordinates for the centroid point of each polygon in the layer.

Tip: The property X returns a field type of double. For best results, your X field should also be a double field type.

This text comes directly from the ArcGIS help window and can be reached by first locating "Fields in tables" in the index and then "calculating values"

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