COME ONE, COME ALL.(The Talk of the Town)

Why here? This thought must have occurred to the citizens of Boston, Athens, and New York this summer as they saw their cities converted, at great expense, into heavily garrisoned holiday camps for hordes of strangers. Home-town promoters of political conventions and the Olympics invariably argue that such mass visitations are an economic boon. The Bloomberg administration predicted that this week's Republican Convention would create thousands of jobs and more than two hundred and fifty million dollars in extra revenue; the mayor of Boston said that the Democrats would generate a hundred and fifty million dollars in extra business (he overestimated by about a hundred and forty million). But by now it's well established that these mega-events, as economists call them, rarely live up to expectations. They bring in some visitors but scare off others. (Because the Republicans are in town this week, the MTV Video Music Awards were moved to Miami.) Post-September 11th security requirements drain treasuries. Locals skip town, and productivity plummets. As a member of the Los Angeles Convention and Visitors Bureau said, after hosting the Democrats in 2000, "On a dollar-for-dollar basis, you'd be better off with a national gastroenterologists' convention."

Still, city planners and Chamber of Commerce types have another rationale for hosting mega-events: you can't beat the publicity. Travel and tourism have become crucial to the economic health of many American cities, where high-wage, low-skilled jobs have disappeared. Tourism is a curious kind of export business--your customers are in other cities and countries, but, instead of shipping the product to them, you get them to come to you. So political conventions are pitched as advertisements for cosmopolitanism and comfort--as weeklong exercises in building a city's brand name.

Cities want the publicity because they need the customers. In the last fifteen years, city planners have been on a construction spree, erecting huge new convention centers, hotels, and exhibition halls. Chicago added a million square feet. Omaha, Baton Rouge, Hartford, and Fort Wayne got in the game. Boston blew eight hundred and fifty million dollars on a gorgeous new palace in South Boston, which sat unused last month as the Democrats gathered in the Fleet Center instead. Cities embraced a version of Say's Law--supply generates its own demand. They assumed that if they built the convention space the conventioneers would come. Well, the boom didn't happen. In the late nineties, Indianapolis added a hundred thousand square feet of convention space and overhauled its domed stadium, but, between 1996 and 2002, the number of conventioneers in town fell by almost twenty-five per cent. The convention business is still big, but the exhibition-hall glut has made it harder ...