I implemented this interactive visualization for a university course about geovisualization. It allows the user to visually compare two variables (either the outcome of a vote or a socio-demographic factor, per district). Two maps are used to show the geographical distribution of the variables, and quartiles are computed to distribute the values into four classes.
A scatterplot allows the user to contrast the two chosen variables and explore possible associations. Both views (map and scatterplot) are linked, so the user always knows which district he or she is dealing with.
On top of that, the user has the possibility to draw a rectangle around the points in the scatterplot and thus select a set of districts ("brushing"). After this, the corresponding districts are highlighted in the map. This helps, for instance, to quickly identify regions where certain variables have high or low values, etc.
In order to better compare differences between subsequent variables, a linear, visual transition of half a second is used. This helps to mitigate the problem of change blindness.