Source: Nelson, A. (2008) Estimated travel time to the nearest city of 50,000 or more people in year 2000. Global Environment Monitoring Unit – Joint Research Centre of the European Commission, Ispra Italy.
Space – time convergence is far from being a uniform process as differences in transport infrastructures and basic landscape constraints have a discriminatory effect on accessibility. The above figure represents travel time, from less than 1 hour to 10 days, to the nearest city of more than 50,000 people. It is the outcome of an overlay of several friction of distance factors, including the road and rail networks, navigable rivers, shipping lanes and land cover. It can be considered as a proxy for global accessibility with only 10% of the world’s population being more than 48 hours away from a large city. While it depicts the general ease of accessing urban markets, it does not depict well the effectiveness of global freight flows. For instance, while South Asia appears highly accessible because of the density of large cities, the quality and capacity of inland transport infrastructures is generally poor.