Citizens have long wondered how often their governments ask online service providers for data about users, and how often governments ask providers to take down content. Today Google took a significant step on this issue, unveiling a site reporting numbers on a country-by-country basis.

It’s important to understand what is and isn’t included in the data on the Google site. First, according to Google, the data excludes child porn, which Google tries to block proactively, worldwide.

Second, the site reports requests made by government, not by private individuals. (Court orders arising from private lawsuits are included, because the court issuing the order is an arm of government.) Because private requests are excluded, the number of removal requests is lower than you might expect — presumably removal requests from governments are much less common than those from private parties such as copyright owners.

Third, Google is reporting the number of requests received, and not the number of users affected. A single request might affect many users; or several requests might focus on a single user. So we can’t use this data to estimate the number of citizens affected in any particular country.

Another caveat is that Google reports the country whose government submitted the request to Google, but this may not always be the government that originated the request. Under Mutual Legal Assistance Treaties, signatory countries agree to pass on law enforcement data requests for other signatories under some circumstances. This might account for some of the United States data requests, for example, if other countries asked the U.S. government to make data requests to Google. We would expect there to be some such proxy requests, but we can’t tell from the reported data how many there were. (It’s not clear whether Google would always be able to distinguish these proxy requests from direct requests.)

With these caveats in mind, let’s look at the numbers. Notably, Brazil tops both the data-requests list and the takedown-requests list. The likely cause is the popularity of Orkut, Google’s social network product, in Brazil. India, where Orkut is also somewhat popular, appears relatively high on the list as well. Social networks often breed disputes about impersonation and defamation, which could lead a government to order release of information about who is using a particular account.

The U.S. ranks second on the data-requests list but is lower on the takedown-requests list. This is consistent with the current U.S. trend toward broader data gathering by law enforcement, along with the relatively strong protection of free speech in the U.S.

Finally, China is a big question mark. According to Google, the Chinese government claims that the relevant data is a state secret, so Google cannot release it. The Chinese government stands conspicuously alone in this respect, choosing to deny its citizens even this basic information about their government’s activities.

There’s a lot more information I’d like to see about government requests. How many citizens are affected? How many requests does Google comply with? What kinds of data do governments seek about Google users? And so on.

Despite its limitations, Google’s site is a valuable step toward transparency about governments’ attempts to observe and control their citizens’ online activities. I hope other companies will follow suit, and that Google will keep pushing on this issue.