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Quantitative information on regional or local market integration is scarce. Summary statistics—such as the road length in a state or province or the straight-line distance to ports or urban agglomerations—are poor proxies for the complexity of a national or regional transportation network. To improve on them, a geographic representation of Mexico’s transport network is used to compute an index of accessibility for each municipio in the country as a simple measure of potential market integration.

This index summarizes the size of the potential market that can be reached from a particular point given the density and quality of the transport network in that region. For any point in the country, it is the sum of the population of urban centers surrounding that point, inversely weighted by the travel time to reach that center. It is computed using an up to-date digital map of transportation infrastructure from the Mexican statistical agency (Instituto Nacional de Estadística y Geografía, INEGI).(a) For each road segment, the database indicates the number of lanes and whether those lanes are paved or unpaved—and for railroad lines, the number of tracks. For each category of road or rail, average travel speeds are estimated to calculate how long it will take to traverse each segment in the transport network. (b) Urban population data from the INEGI database indicate the location and population size of about 700 cities and agglomerations in Mexico. These urban centers accounted for about 68 million of Mexico’s 97 million people in 2000.

Click to enlarge The map of market access shows high values of the index around the federal district, thanks to concentrations of people and infrastructure. A quarter of Mexico’s GDP is generated within two hours’ travel time from the center of the Federal District. The southern states of Chiapas, Guerrero, and Oaxaca, the poorest areas, have low market access. Source: Deichmann, Fay, Koo, and Lall 2004. a. The digital road and rail network includes 171,000 kms of roads, of which 84,000 kms are paved roads; 51,000 are unpaved; and 36,000 are paths and breaches. The rail network has an estimated total length of 14,000 kms. These values are calculated by a geographic information system (GIS) from 1:1 million scale digital maps and may not necessarily match official statistics. b. Using travel time on a transport network provides a more accurate measure of accessibility compared with the computationally much simpler straight-line distance, as employed, for example, by Hanson (1998). Â