How to populate table with sums of values in another table?

Hi all,

I have population breakdowns for ca. 100 geographical subdivisions of a country in a table, and I need to express this breakdown in ca. 30 subdivisions under which my the 100 subdivisions nest. I was about to manually create the correspondence by simply saying that say that for each 30-sub (listed in a column), a given cell, say AA2, "=A2+A6+A30" (the 100-subs are also in a column), for another, say AA3, "=A40+A56+A82", and so on; and then copying across the columns for the different elements into which the population has been broken down. But this is arduous and also liable to break if the first table ever gets re-ordered.

What I need is to tell Excel to associate row names between each of the tables. So I tell Excel that one 30-sub geography, say "Dublin," comprises three geographies in the 100-sub table, say "S Dublin," "N Dublin," and "C Dublin," and that it should sum the value in those rows.

But I can't think of what the command would be. Thanks in advance!

EDIT: I just worked it out. Too straightforward to mention. Simply created another row in the original (100-sub) table with the 30-sub categories. Then PivotTable.