We are now prepared to extend to urban rents, with some modification, the principles we have just learned. Obviously, fertility is not a factor in determining the selection of an urban site. Hence, location alone will claim our attention in this discussion. Urban sites might be divided into an infinitely large number of groups, but for our purpose two will suffice: residence sites and business sites. It is a matter of common knowledge that some store sites more than others are desired by merchants. Usually the determining factor in retailing is the size of the crowds that pass certain points during the day. A department-store owner has the option of utilizing a site near a busy down-town corner, or he may locate his stock of goods somewhere in the residence district, or even out in the desert, where land is free for the asking. We may say at once that if he is a wise merchant he will not try to operate his store in the residence district, certainly not in a desert. Here we have the principle of site rent. The down-town business lot, like our best located farm on the island, enjoys the best location. For that reason it yields economic rent. Superior urban sites, like agricultural lands above no-rent land, yield economic rent though the owners themselves utilize them. If the owner and the utilizer are different persons, the economic rent takes the form of contract rent. Otherwise it becomes a part of the utilizer's total income.