Welcome to Part 6 in a continuing series on the political geography of the states. This segment looks at the county trends in statewide elections across multiple election years in most of the states. Given how most downballot elections occur in non-presidential years, I'll only be comparing elections in the same type of cycle to reduce the impact of different turnout dynamics, so trends will measure the change between 2006 and 2010 or 2008 and 2012. Since many states saw 2006 be very friendly to Democrats while 2010 was very favorable to Republicans, there is a fairly clear pattern of the Dem base areas trending Democratic, especially if they're heavily minority, reflecting the relative inelasticity of those voters. In constructing the following maps, I looked at the average of the Democratic percentage for D vs R partisan statewide elections by county and how that percentage varied from the statewide percentage over the two cycles. Note that when I say a county or district trended Democratic or Republican, it is relative to the state as a whole, not in absolute terms.
You can find the previous installments on the individual states grouped by the 4 census bureau regions here (the West, the Mid-West, the Northeast, the South) and Part 5 on the national elections for the US Congress. The data used to construct all of these maps can be found here.