Location is the most important factor for retail success. There are different types of store locations including shopping centers, city locations, and free-standing sites. Factors that affect the attractiveness of a site include demographics of the trade area, accessibility and traffic flow, and proximity to complementary retailers. Methods for evaluating potential sales at a new location include analyzing customer spotting data, census data, competition, and using Huff's gravity model to calculate the probability of customers shopping at the new location based on its size and their travel time.