four tiers--town, small, intermediate, and large city--based on travel time using a global travel friction grid, acknowledging that individuals may rely on multiple centers for various needs, with larger centers offering a wider range of activities. The dataset, classifying over 30,000 urban centers into the four tiers, is publicly available.

Examples

*Airports can be built and maintained in locations which minimize the driving distance for the surrounding population to reach them.
*A

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