It's very simple actually. For instance, let's assume Walmart automotive takes maybe 2-3 FT employees to operate, where this may normally be fragmented across 2-3 local mechanics employing 3-6 FT employees each. Then of course you have the 2-3 local services which catered to them (E.g. cleaning services, real estate agents, CPAs, ect). Then, multiply this for each Walmart department (Electronics, Groceries, Pharmacy, Auto, Household, ect.) and there's your town.