You can use calculated members to aggregate a custom group of dimension members. For example, you can create a calculated dimension member that sums a group of cities in California.
CREATE member \[Sales\].\[Customers\].\[All Customers\].\[USA\].\[CA\].\[City Group\] AS 'Aggregate(\[Altadena\],\[Arcadia\],\[Bellflower\])'
After you execute the CREATE member statement, you can use \[City Group\] as a shortcut to the sum of the three California cities. How would you rewrite the above statement so that \[City Group\] is a shortcut to the same set of three California cities? This time you don't want the sum. You want to list all three cities each time you use the name \[City Group\].