Neat:

The CEPII has built and made available two datasets providing useful data for empirical economic research including geographical elements and variables. A common use of these files is the estimation by trade economists of gravity equations describing bilateral patterns of trade flows…

Distance calculation requires information on geographical coordinates of at least one city in each of the country. The simplest measure of geodesic distance considers only the main city of the country, reported here with the English and French names, latitude and longitude. In most cases, the main city is the capital of the country. However, for 13 out of the 225 countries, we considered that the capital was not populated enough to represent the “economic center” of the country. For these countries, we propose the distances data calculated for both the capital city and the economic center…

There are two kinds of distance measures: simple distances, for which only one city is necessary to calculate international distances; and weighted distances, for which we need data on the principal cities in each country. The simple distances are calculated following the great circle formula, which uses latitudes and longitudes of the most important city (in terms of population) or of its official capital. These two variables incorporate internal distances based on areas provided in the geo_cepii.xls file. The two weighted distance measures use city-level data to assess the geographic distribution of population inside each nation. The idea is to calculate distance between two countries based on bilateral distances between the largest cities of those two countries, those inter-city distances being weighted by the share of the city in the overall country’s population.