The greatest divide between denizens of digital and physical worlds is generational: according to Pew, 93 percent of 18-to-32-year-olds use the Internet, while only 38 percent of 65+ Americans are online. Beyond age, the Internet population is richer, better educated, and whiter than the general population. When you look at the most influential, active, or politically engaged Internet users, these discrepancies are even more stark. These skews suggest that issues and political opinions favored by the young, rich, educated, and white get more traction online than elsewhere.

The Internet has made group formation easier than ever and provided an outlet for ostracized minority groups--sometimes for the first time. But online demographics help determine the strength of these communities. Younger generations have leaned towards the Democratic party for the past few decades; the netroots has no conservative equivalent, not because Republicans aren't politically active, but because the conservative base is older and less likely to be online.

The young are more libertarian, pro-marijuana, and less religious than the American population generally. Millennials (pdf) are gay-friendly, racially tolerant, technologically savvy, welcoming of immigrants, open to government intervention, less hawkish, more accepting of non-traditional families, less inclined to marry early, and more optimistic about the state of the state of the nation. Thus, the consensus view among American Internet users may differ substantially from the result at the ballot box.

This incongruity is amplified because senior citizens, the demographic least likely to have a robust online presence, has an outsized electoral footprint. 72 percent of American 65-to-74-year-olds voted in the 2008 election while only 48.5 percent of 18-to-24-year-olds exercised that right. We are in an era when the young have the most control over the dominant cultural medium while the old have the greatest say politically.

This power imbalance also exists internationally. During last year's protests in Iran, Twitter was a primary means of receiving news from inside Iran. But how representative of the Iranian population were those tweeters? A few weeks after the protests broke out Sysomos found that 93 percent of Twitter users were located in Tehran, the center of the protests and one of Iranian opposition leader Mir-Hossein Mousavi's strongest bases of support.

It's hard to get an accurate picture of online populations because Internet users self segregate into ideological camps. Deciphering the discrepancies between the physical and digital realms is made more difficult by privacy considerations and technological barriers. But conducting a census of American Internet users doesn't require government intervention; e-marketing and American opinion organizations are already performing much of the necessary research. What's needed is better organization and easier access to this information. As digital devices become the primary method of interacting with the world, there is a growing need for the wide dissemination of accurate and prompt statistics about the ideological composition of the Internet, and how it differs from the world beyond the screen.