You have probably heard it asserted that Mahmoud Ahmadinejad principal strength is in rural areas, whereas Mir-Hossein Mousavi did relatively better in Iran’s cities. However, it is not clear that this is true. Moreover, in 2005, it is demonstrably false. On the contrary, Ahmadinejad did much better in urban areas in that election.
I was finally able to track down data on the urbanization of each of Iran’s 30 provinces, as listed on the website of the Statistical Center of Iran. Although Iran is a fairly large country, most of its population — about 68 percent — lives in cities. Its population density is quite comparable to that of the continental United States.
The percentage of Iranians living in urban areas in each province follows below:

Now, let’s compare that to the percentage of the vote that Ahmadinejad received in each province in the first round of the 2005 election:

This is, obviously, a rather strong correlation. In 2005, Ahmadinejad was a man of the cities. Iran’s most urban province, the small province of Qom (or Ghom), is also where Ahmadinejad got his largest share of the vote (55.2 percent) in the first round of the 2005 elections. Ahmadinejad’s performance was quite not as strong in Tehran province, where he got 30.1 percent of the vote, but that was still better than the 20.3 percent he got overall, which was just enough to place him second and qualify him for the run-off.
Now, let’s contrast that to what happened on Friday:

The correlation disappears, although it does not actually reverse itself. While Ahmadinejad did relatively poorly in some urban provinces like Tehran and Yazd, he did well in others like Qom and Ishafan.
So it’s not exactly correct to say that Ahmadinejad’s strength was in rural areas. What we certainly can say, however, is that almost all of the improvements that Ahmadinejad made over his 2005 totals came in rural areas. What was once a weakness of his turned into another strength.
This means that at least one of two things must be true. Either the urban-rural dynamics of Iran have changed significantly over the last four years — at least insofar as it they affected perceptions of a candidate like Ahmadinejad. Or, alternatively, the election was rigged, and those who rigged it for some reason decided that rural votes were easier to steal.
Gallup polling conducted in 2008, incidentally, found that rural Iranians expressed much more confidence in the integrity of Iran’s elections:

Again, I don’t think this proves much of anything in and of itself; both explanations I outlined above are entirely plausible. But if you’re going to steal votes, it is probably advisable to do so people who are less likely to notice that you’re stealing them. In Iran, that means people in rural areas.