As the Wisconsin Senate debates the proposed voter ID bill (SB 6), which requires a valid photo ID to vote, I was interested in the spatial distribution of disenfranchisement that might occur. Unfortunately, there’s little detailed data on registered voters and drivers licenses that’s publicly available for a comprehensive analysis. As a proxy, I’ve compared the number of valid drivers licenses from the Department of Transportation (available here for 2009) to the number of registered voters from the Government Accountability Board (available here for 2010).
Interpretation of this map requires caution for several reasons: 1) it doesn’t include all forms of ID that can be used (e.g. military IDs) for which detailed data isn’t available, 2) many drivers have licenses without a current address, 3) many drivers are not of voting age, and 4) the data are not from the same year.
Several counties (Dane, Milwaukee, Ozaukee, and Door Counties) have more voters than drivers, meaning that currently registered voters within these counties will have to obtain new IDs to vote. The total voters without drivers licenses within these counties, 20,162 voters, is well within the margin of recent elections. The largest numbers are from Dane and Milwaukee Counties which have traditionally voted heavily for the Democrats. Will there be a differential impact on future elections?
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It's academic 
Also please don’t forget about us that are temporarily living abroad. We’re working with a university here in New Zealand, and won’t be able to fly back to Wisconsin to get IDs updated before the next election.
We know others from Wisconsin; scientists working on Antarctic research and students on study abroad just to name a few who are in the same predicament. Emails to my representatives about how we might be able to vote in the future have gone unanswered.
Wondering if you have a reply yet on absentee voting…
If you are New Zealand or Antarctica won’t you be voting by mail?
I believe if you are voting by mail you must include a photocopy of a valid ID with your ballot. So if your ID is not correct they would not count your vote.
This is an excellent tool that people who are interested in how laws affect voting patterns. It appears to me that this law will affect the voting rights of particular classes of people and cannot possibly hold up in court!