polys.plot: Plot geographic regions defined as polygons

Description

Produces plots of geographic regions defined by polygons, optionally filling the
polygons with a color or grey shade dependent on a covariate.

Usage

polys.plot(pc,z=NULL,scheme="heat",lab="",...)

Arguments

pc

A named list of matrices. Each matrix has two columns. The matrix rows each define the
vertex of a boundary polygon. If a boundary is defined by several polygons, then each of these must be
separated by an NA row in the matrix. See mrf for an example.

z

A vector of values associated with each area (item) of pc. If the vector elements
have names then these are used to match elements of z to areas defined in pc. Otherwise
pc and z are assumed to be in the same order. If z is NULL then polygons are not filled.

scheme

One of "heat" or "grey", indicating how to fill the polygons in accordance with the value
of z.

lab

label for plot.

...

other arguments to pass to plot (currently only if z is NULL).

Value

Simply produces a plot.

Details

Any polygon within another polygon counts as a hole in the area. Further nesting is dealt with by
treating any point that is interior to an odd number of polygons as being within the area, and all other points
as being exterior. The routine is provided to facilitate plotting with models containing mrf smooths.