[Atlas Sneezed]

Houston looks pretty red to me, although I don't understand why it appears so short in comparison to much smaller cities like Pittsburgh.

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That's because the "height" is based on the total margin of victory. Notice that Reno and Albuquerque (in 51-47 counties) are essentially absent.

[Dog Gone]

Bush won by more in Houston than Kerry did in Pittsburgh, so that ain't it. And it isn't really proportional margin, or you'd see gigantic cities all over the map.