I'll start with 2008-2012
Scale:
I was experimenting with the partisan trends and turnout differences; I've made national maps for both in the past, but wanted some way to combine them. Homely's
race/party maps provided a good starting point for working out my color scheme
Basically, the darker counties on this map cast more votes in 2012 than they did in 2008. As turnout was lower nationwide, the majority of counties are lighter, meaning fewer votes cast. Likewise, counties that trended Democratic are a pinker shade of purple while Republican-trending counties are bluer/violet.
An ideal situation for Democrats would thus be something like Maryland or southern TX: darker shades of pink = higher turnout + favorable trend. Utah and western ND would be some of the best results for the GOP here.
Hopefully, I'll be making this into somewhat of a series with more maps