Municipal officials and terrorism experts did a double-take recently when Boise, Idaho, showed up near the top of a list of cities most vulnerable to terrorism -- the only city in the western U.S. to do so. Of greater interest to Virginians, however, is the fact that two cities in the commonwealth also appear on the list: Norfolk and Richmond.

Funded by the Department of Homeland Security, the study in the journal Risk Analysis relies on four years of research and advanced mathematical modeling techniques. It ranks 132 American cities not on how likely a terrorist attack would be in a given city, but how well a city could withstand and react to an attack. "You can't predict the next [terrorist attack]," said one of the study's authors. "That's why it's terrorism. But you can predict vulnerability."

Cities used to handling disasters -- such as earthquake-prone California burgs -- fared well. So did cities with lower population density. As one news story summarized, "a city with well-built bridges might find itself higher on the list if its high-density population makes evacuation difficult." Norfolk ranks No. 5 on the list. Richmond made the top 20.

Virginia's government agencies, at both the state and local level, have worked hard to make the state and its subdivisions safer, and continue to do so. The Old Dominion is fortunate to have several advanced medical colleges and numerous military installations, too. But some of the characteristics that make Virginia such an excellent place to live also complicate the business of emergency preparedness. Imagine, say, the effect on Central Virginia of Hurricane Isabel, but with radioactive fallout and a blast crater.

One study doesn't offer the last word on terrorism preparedness. But it does provide a useful reminder of its importance.