I’m a big fan of Nate Silver and his 538 blog. In a recent post, he highlighted the increase in partisanship in the House of Representatives. Silver used this horizontal stacked bar chart to drive home his message:
He categorized congressional districts by the amount their presidential vote was over the national vote. For example, landslide Democratic districts were at least 20 point higher in their votes for the Democratic presidential candidate than the national average.
Silver did a great job with colors, using shades of red and blue to depict strength of Republican and Democratic votes in a district. Your eye is quickly drawn to the funnel of increasing dark red and blue and decreasing yellow (swing districts) between 1992 and 2012. The blog post goes on to provide more data, including statistical analyses, to support his conclusion, but for me the chart presents the message best.