seafaring

“The Human Mobility Index (HMI)” that estimates the potential minimum travel time across the globe (measured in hours) accounting for human biological constraints, as well as geographical and technological factors that determined travel time before the widespread use of steam power. In particular, the HMI indices provide a distinct measure of human mobility potential in different eras:

Human Mobility Index (HMI): Mobility on land without seafaring technology. Shows mobility potential on land before the widespread use of steam power.
Human Mobility Index with Seafaring: HMI expanded to allow mobility on a select set of seas for which historical data was available. Shows potential mobility on land and seas before the introduction of ocean-faring ships.
Human Mobility Index with Ocean: HMI expanded to allow mobility on all seas based on CLIWOC (interpolated). Shows potential mobility on land and seas after the introduction of ocean-faring ships, but before the widespread use of steamships.
Based on these cost surfaces, researchers can find the minimum travel times between locations or construct more sophisticated statistics based on these. For example, Ashraf, Galor and Özak (2010) construct measures of pre-historic geographical isolation to study the effect of isolation on development. Similarly, Özak (2010), Depetris-Chauvin and Özak (2016, 2020) and Michalopoulus and Özak (2019) construct potential trade and information flow networks among countries, ethnic groups, cities, and artificial geographical units, to study the origins of the division of labor, and the effect of technological change on isolation and development. Likewise, Depetris-Chauvin and Özak (2019) use these measures to construct artificial states based on Voronoi partitions.

This strategy overcomes the potential mismeasurement of distances generated by using geodesic distances (Özak 2010), for a period when travel time was the most important determinant of transportation costs. Additionally, it removes the potential concern that travel time to the frontier reflects a country’s stage of development, mitigating further possible endogeneity concerns. The research validates these measures by (i) analyzing their association with actual historical travel time; (ii) examining their explanatory power for the location of historical trade routes in the Old World; and (iii) analyzing their association with genetic and cultural distances.