Second, the definition can be a framework for all traditional geographic subjects, themes, and traditions. Third, the definition functions at all scales. In studying towns and cities, for example, site (specific location and condition of a place) can often explain their presence. For example, New York City is located at the mouth of the Hudson River with a natural harbor protected by Long Island; San Diego and Seattle are on excellent natural harbors; and Denver is at the eastern terminus of a pass through the Rocky Mountains. South Dakota's largest and fastest growing city, Sioux Falls, affords a splendid example to illustrate the importance of "Where?" When the city was settled in 1856, eastern South Dakota was inhabited by people of the Sioux culture. The city's name, itself, implies the importance of location and place: The falls on the Big Sioux River provided power for a mill around which the city was originally established. Through time, the city grew primarily because of its location in the wettest, hence most agriculturally productive, area of the state. It also served as a major highway and rail hub. Finally, rapid growth continued because of its location at the intersection of two interstate highways.