_Rural-urban gradient in Latin America and the Caribbean_ _page_ 3 Access to major urban centers is another aspect of the urban-rural gradient that captures important determinants of economic opportunities and constraints. Areas within easy commuting radius of a major urban center can for many purposes be considered urban, even if occupied by farmsteads. The edge of this commuting radius may constitute a meaningful break-point or discontinuity on the urban-rural divide, though it is not sharply delineated. At slightly larger radii, farm and nonfarm households may still enjoy some urban employment opportunities, and can profitably grow fruits and vegetables for urban markets. Perhaps there is another meaningful breakpoint, though even less sharply defined, at the von Thünen distance associated with truck farming for urban consumption. As remoteness increases to market increases still further, von Thünen teaches us that activities will systematically change<sup>1</sup> . Households will either move to production of goods with low relative transport costs, or shift towards subsistence production. There will also be a strong though not universal tendency for population density to decline as remoteness increases.

Figure 1, taken from Chomitz and Nelson (2003), illustrates the rural urban gradient in the context of Nicaragua. Based on municipio-level data it shows the strong correlation between travel time to Managua, incidence of severe rural poverty, and low population density (all measured in logs). The tightness and smoothness of the relation is remarkable. However, the graphs exclude the six municipios of Managua Department, which show a sharply lower poverty rate than would be predicted by travel time alone.

Areas towards the rural end of the density and remoteness gradient are by no means homogeneous. Rural development policies may be profoundly influenced by two important environmental factors: agroclimatic suitability for cropping, and current forest cover. These factors are important determinants of the prospects for agriculturally-led rural development, and of the potential effect of development on environmental externalities. Both factors are best viewed as continuous variables.

In summary, we propose to define urban-rural gradients along two dimensions: population density, and remoteness from large cities. Two subsidiary additional dimensions will be used to characterize populations and land areas: agricultural suitability and forest cover.

# **Data for construction of rurality gradients**

## **Population density**

Population density is a scale-dependent concept. The population density at a point is, in principle, the mean number of persons per square kilometer evaluated within a radius r of the point and thus should vary continuously over the landscape. The choice of r depends, ideally, on the application for which density is needed. For many of the infrastructure and service delivery issues mentioned above, r might be on the order of a few to several kilometers.

> 1 In reality, land use is affected not just by market distance, but by soil and climate conditions.  For this reason, clearly-delimited von Thünen rings are not always observed.  See Chomitz and Gray (1996) for an empirical land use model of Belize that incorporates both market access and agroclimate in explaining the allocation of land between commercial farming, subsistence farming, and forest.