If you listened to the election returns or watched it on TV, you watched the red vs. blue US map take shape and heard, again and again, "Gosh - it looks just like it did in 2000." They didn't realize just how much it looked the same.
This map paints black all the counties that voted either Republican or Democrat in 2000, and voted the same in 2004. Red counties are those that switched from Democrat to Republican. Blue counties switched from Republican to Democrat.