The other day I came across an interesting study of the urban hierarchy in the United States.
It dealt with the functional integration of 46 large cities in the national urban system as measured through the intensity of information flows.
This was an exceptional study because it focused on how cities relate to each other rather than on simple attributes (number of company headquarters, etc.).
The study measured the position of U.S. cities in the national urban network through the role of air courier services, a good example of producer services that are increasingly important in the new economy.
Air courier services deal with overnight mail deliveries and most of their business is with corporate clients. Such mailings often contain important and timely information.
The authors of the study argue that the generation of information and the issuing of "commands" is a good measure of the centrality of cities in the national urban system.
The study used data from Federal Express, the largest company of its kind in the United States, from 1982 to 1994.
To no great surprise, New York is by far the largest generator of information of all U.S. cities. Los Angeles comes in second and Chicago is third. Miami ranks 10th among all metropolitan centers in the United States.
What is especially interesting is that over time, New York became ever more dominant and more central. In the early '80s, New York was the most important information origin for 22 of the 46 cities; 10 years later, this number had risen to 30.
The study also nicely illustrates the relationship between New York and Miami.
Information flows from New York to Miami constituted one of the fastest growing flows in the country. Furthermore, Miami is becoming increasingly subordinate to New York: flows from New York to Miami are growing faster than vice versa.
The large net reception of information from New York suggests that New York "talks" and Miami "listens."
But a study of the U.S. national urban system is bound to underestimate Miami's international functions.
Moreover, it is likely that Federal Express's market share in Miami is significantly lower than in other cities like Chicago or New York (the company declined to confirm or deny this).
The Yellow Pages of Metropolitan Miami lists an overwhelming 170 air courier service companies in addition to Federal Express, quite possibly the largest number of any city in the United States.
By comparison, the number for the New York metro area (with an economy much larger than Miami's) is 52. The nature and number of Miami's air courier services illustrate the exceptional position of this city.
Most Miami companies are fairly small and were established in the '70s and '80s.
They took advantage of the growing number of Hispanic businesses with international connections to Latin America and the Caribbean. Many specialize in one or two specific routes and their names often reveal this: Jamaica Air, Maya Express, or Ecua-Peru Courier Services to name just a few.
It is quite an impossible task to combine the figures for all these companies and analyze the direction and intensities of these information flows.
But it seems quite obvious that Miami has a substantial surplus (i.e., it sends much more information than it receives).
Thus, a study of the U.S. national urban system can only capture a part of Miami's position. It reveals Miami's vital and dependent link to New York in the world city hierarchy, but it fails to show what happens one step down the hierarchy.
When Miami "talks," Caribbean and Latin American cities "listen."
Jan Nijman is professor of Geography and Regional Studies at the University of Miami.