An enterprising soul has drawn up a county-by-county electoral map for the 2008 Democratic primary between Barack Obama and Hillary Clinton. It’s most interesting because it allows you to look at where each candidate has concentrated support without regard for state borders.
Click on the link for a larger map
The map is imperfect because different states vote at different times and in different formats, so you see things like Clinton shoring up support in Northern and SW Missouri vs. their demographically similar counterparts in Southern Iowa and SE Kansas. Still, it’s striking how Obama dominates the Missippi Valley, except for parts of Missouri, especially the Bootheel. Even in Arkansas, the only state where Clinton broke 60% of the vote, Obama managed a majority in a few counties on the Mississippi.