A nodal region is an area organized around a node, or focal point, and is defined by interactions or connections. A metropolitan area is an example of a nodal region, such as the Chicago Metropolitan Area, which extends into several counties in Illinois, as well as Wisconsin and Indiana.
The main node in a nodal region features surrounding areas that are linked to it by transportation and communication systems. The main node also has a sphere of economic and social influence that becomes less pronounced at points farther away from it. For example, a behavior that is acceptable in Chicago proper, may not be acceptable on the edges of the metropolitan area.