The theory of market-area analysis is useful in the analysis of supply areas. Supply areas are analogous to market areas except that in market areas, products are distributed from a central place or point. In a supply area, a variety of products are brought in from many sources. For example, farmers scattered throughout a region haul a variety of products to a central location. Thus, grain elevators buy produce from many farmers in a given supply area. The elevators clean and store the grain, and at some point send it on to retailer outlets, mills, breweries, and so on. In this case, the supply area is the area served by a particular grain elevator. The farmers that sell their grain to an elevator are situated in its supply area.