This population threshold is drawn from both the town center where the business is located and also from the surrounding rural market area. Because costs of doing business vary by type of business, different products or services will have different thresholds. The consumer's price includes not only the price of the product but also the consumer's costs in traveling to the business. As the distance the consumer must travel to a market increases, the total price to the consumer for each product purchased at that market increases. For example, most people shop for groceries within a few miles of their homes but will travel farther to shop for televisions.
Different products have different market ranges.
Different thresholds and different market ranges lead to a central place hierarchy of towns based upon the number of different types of products sold in each town. Trade-center specialization alludes to the fact that it is more efficient to supply some products from small centers while it is more efficient to supply other products from larger centers. Numerous studies have shown a relationship between the population of a central place and the numbers and types of businesses located in that central place. The higher-order center is larger in population and market area and also supplies more specialized products, for example, bicycle stores and hobby shops. One such mapping of central places and their trade areas is presented in Decongesting Metropolitan America, from which the figure below is drawn.