quite possibly... however vote margin is closely related to population would you not agree?
Not at all. Houston is the 4th largest city in the country and went for Kerry, but the surrounding small towns in Harris county made Bush the winner by a small margin. Look how short the Harris County red pillar is compared to much smaller cities with blue pillars.
It's numeric margin. So if a county with 300,000 voters went 149,999 Kerry and 150,001 Bush, the graphic would be nearly flat with a margin of 2. But the county next door could have say, 54,000 voters, but it was 43,000 Bush to 11,000 Kerry--a margin of 32,000. The smaller, less densely populated county would have a larger, higher graphic.