IF YOU FOUND YOURSELF, during the holiday season, whiling away some of your time in the Dayton, Ohio, airport, you probably found to your surprise that you weren't alone: the Piedmont concourse there was full of people. That's no accident. Dayton has now become one of Piedmont's "hubs" (the others are Charlotte, N.C., and Baltimore), the centers from which most of the airline's flights set out. Since the deregulation of the airlines, the hub pattern has been used by more and more airlines; it is now almost the standard route pattern. American's major hub is Dallas-Fort Worth: most of its flights end up there, and most DFW flights have been American since Braniff, which also used DFW as its hub, went bankrupt. St. Louis is TWA's major hub, and Houston is Continental's; Denver is a seat of competition between United, Frontier and Continental. Smaller airlines, like Piedmont, have taken small and underused airports such as Charlotte and Dayton and made hubs out of them.

The hub pattern was pioneered by Delta in Atlanta and is one of the reasons for Delta's longtime prosperity and for Atlanta's status as the nation's busiest airport. Other major airlines in the 1960s and 1970s had east-west route systems, with American running diagonally across the country and United pretty much straight across, just north of TWA's system. East-west flights captured our imagination since the days of Charles Lindbergh and Wrong Way Corrigan; and even before airplanes, railroad men constructed so many east-west lines that almost all of them went bankrupt while the nation's single north-south line, the Illinois Central, never did.

There has been heavy competition among airlines on these routes, even in the days of regulation. Delta, based in then-unglamorous Atlanta, was shrewd enough to construct another system in which it had less competition and usually made more money. The idea is that most people coming into the hub on Delta flights also fly out on Delta flights, generating lots more money from Delta. By way of comparison, if you wanted to go to some small city in the Midwest in the old days, you might take United or American or TWA to Chicago, and then switch to some other carrier.

Overall, this means more competition among medium-sized cities to become hubs. The prizes are big: much of Atlanta's booming commerce depends on the preeminence of its airport, just as Chicago achieved major-city status when it became a terminal point for many of the nation's railroads. It may come to the point that some cities root for their airlines with the ferocity they now devote to their sports teams. Washington, in the meantime, is a hub only in the sense that it is a major league baseball town: Piedmont's BWI hub, like Memorial Stadium's Orioles, really belongs to Baltimore.