Atlanta's underground sex trade is larger than Seattle, D.C., and Denver's combined. The price of a sex act in major U.S. cities can range anywhere from $15 to considerably more than $1,000. More pimps shell out for transportation and housing than for hotels or clothes.

Those are just a few of the insights gleaned from a massive new government-sponsored study from the Urban Institute on the underground economies of sex, drugs, and guns in eight cities: Atlanta, Dallas, Denver, Kansas City, San Diego, Seattle, and Washington, D.C.

Lead researcher Meredith Dank spent three years talking with former pimps, sex workers, and law officials. "Having done research in this field for many years now, it answers a lot of stuff that we only knew anecdotally, but it also debunks some of the myths that get talked about within media and advocacy work," she told National Journal. For example, the report finds that coercion and encouragement from family members to make money was a bigger factor in persuading women to go into (and stay in) prostitution than physical violence.

Here are eight facts from the report. Most of the statistics are from 2007, recorded in 2005 dollars.

1. Atlanta has the biggest sex economy among the studied cities, by far. Dallas has the largest market for drugs or guns. It's important when considering this chart from the New York Times to know that these figures compare cities whose gross metropolitan products range from $420 billion in Dallas to $167 billion in Denver. More useful might be share of the cash market...