Exploring Data in Two Dimensions

Polygon Plots

This section describes how to use a polygon plot to visualize map data. A polygon plot displays polygons that are linked to levels of one or more categorical variables.

The polygon plot can display arbitrary polylines and polygons. To create a polygon plot, you need to specify at least three variables. The coordinates of vertices of each polygon (or vertices of a piecewise-linear polyline) are specified with X and Y variables. The polygon is drawn in the order in which the coordinates are specified. A third nominal variable specifies an identifier to which each coordinate belongs.

In some instances, a polygon is composed of subpolygons. For example, a continent is composed of countries, a country is composed of individual provinces or states, and some of those states are composed of disconnected landmasses (such as islands). The polygon plot supports this hierarchical structure by allowing multiple nominal variables that identify the continent, state, and island to which each coordinate pair belongs.