Admiral FCS, on 8 Dec 2010, 4:17, said:
I've got the Census Repository Building. Now I'm wondering what's cap.
Try hovering the mouse over numbers in the query itself and you will see the descriptions.
It is used to determine if your region has reached the population caps. If your cities experience stagnant growth, then mostly probably they have reached the population cap (100%), which can be relieved by building additional recreational parks, airports etc, depending on the type of the population (Residential, Commercial or Industrial).