Mastering Data Analysis with R

Rendering polygons around points

Besides thematic maps, another really useful way of presenting spatial data is to draw artificial polygons around the data points based on the data values. This is especially useful if there is no available polygon shape file to be used to generate a thematic map.

A level plot, contour plot, or isopleths, might be an already familiar design from tourist maps, where the altitude of the mountains is represented by a line drawn around the center of the hill at the very same levels. This is a very smart approach having maps present the height of hills—projecting this third dimension onto a 2-dimensional image.

Now let's try to replicate this design by considering our data points as mountains on the otherwise flat map. ...