If no arguments are passed, defaults to plotting the sampling weights for
the redist_plans object. If no weights exist, plots district
populations.
# S3 method for redist_plans
plot(x, ..., type = "distr_qtys")the redist_plans object.
passed on to the underlying function
the name of the plotting function to use. Will have
redist.plot., prepended to it; e.g., use type="plans" to call
redist.plot.plans.