Illinois is the most populous and demographically diverse Midwestern state and the fifth most populous state in the nation. With Chicago in the northeast, small industrial cities and great agricultural productivity in central and western Illinois, and natural resources like coal, timber, and petroleum in the south, Illinois has a broad economic base. Illinois is an important transportation hub; the Port of Chicago connects the Great Lakes to the Mississippi River via the Illinois River. Though Illinois lies entirely in the Interior Plains, it has three major geographical divisions. The first is Northern Illinois, dominated by the Chicago metropolitan area, including the city of Chicago, its suburbs, and the adjoining exurban area into which the metropolis is expanding. Southward and westward, the second major division is Central Illinois, an area of mostly prairie. Known as the Heart of Illinois, it is characterized by small towns and mid-sized cities. The third division is Southern Illinois, comprising the area south of U.S. Route 50, and including Little Egypt, near the juncture of the Mississippi River and Ohio River. This region can be distinguished from the other two by its warmer climate, different variety of crops (including some cotton farming in the past), more rugged topography (the southern tip is unglaciated with the remainder glaciated during the Illinoian Stage and earlier ages), as well as small-scale oil deposits and coal mining.