Creating faceted maps

Bringing facets to maps will require a little more work with respect to the data manipulation. Departing from the experience handed down byChapter 6, Crafting choropleth maps using ggplot2 recipe, this recipe will draw a faceted choropleth containing two years, 1970 and 1986, of US gross states production (gsp).

Basically, what we will need is to have the whole coordinates data frame duplicated, one for each combination given by the facets, in this case only two. This recipe will teach how to manipulate data in order to make faceted maps.

Getting ready

Data is coming from the Ecdat package and dplyr is used to deploy some data manipulation; check whether both are already installed:

> if( !require(Ecdat)){ install.packages('Ecdat')}
> if( !require(dplyr)){ install.packages('dplyr')}

With these ready, we can manipulate data to create a faceted choropleth.

How to do it...

Creating faceted maps is done as follows:

1. Load ggplot2 and the US map:

> library(ggplot2) 
> us_map...