Gravity-consistent aggregate distances (harmonic, geometric and arithmetic mean) between countries and other geographical entities computed using nighttime lights data as weights. In most applications the use of the harmonic mean distance (theta = -1) is recommended. Similarly, often time-invariant distances are sufficient, e.g. those with weight from the year 2000.
Note that EU NUTS regions include those of candidate countries as well as of the UK. US states include Washington, DC and Puerto Rico.
For more detailed data with thetas ranging from -2 to +1 the use of the R package gravity.distances is recommended.
If you need gravity distances between geographic entities not listed above that could also be of interest to other researchers, please send me an e-mail. Maybe we can work something out: mail@julianhinz.com