Here is a fun little Twitter tool that should give you a little more insight into who is following you.
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TweepsMap connects to your account and analyzes where your followers are (based on listed location), then gives you the results in map and list form. You can also drill down on the results and show country, state and city results.
You may actually find out something new with TweepsMap. For example, I always assumed the majority of my followers were within my region. I was surprised to see the first New England state on my list was Massachusetts at number 5. Also, I found that only 51% of my followers were located in the U.S. I always assumed that percentage was higher.
Try it out. You will probably be surprised at the results.