Node

A node (sometimes called a vertex in graph theory) is the basic unit of a graph. A graph consists of a set of nodes along with links (or edges) to connect them.

When a map is converted to a graph, each area on the map must be converted to a node. The node represents the area and is used to determine the connections between areas. In order to determine the connections, the node is associated with a single point in the area.

Since most of the areas on a map represent political units, the node for that area is the political center of that unit. Typically that is where the political body for that area meets. For a county the node is the county office where the elected officials meet. For a city or town the node is the city or town hall. For VTDs that are precincts, the node is the polling place in that precinct.

A district plan will sometimes involve a chop of a county or city that results in an area that is not a single political unit, or is a unit without a political center. In this case the node for that area is the location of the greatest population density in that area.