We shipped off the 1:15,000,000 scale first-order administrative units for Natural Earth Vector to University of Wisconsin @ Madison to be attributed with country and province names and alpha-numeric codes last week. There are only 3,000+ of these around the world so this is no small task! Kudos go to Tom for doing the heavy lifting on this data theme. Props to Kevin and Ben @ UW-Madison for undertaking the attributing.
Some units are super tiny (see Slovenia in the Europe detail at bottom, almost equivalent in scale to municipalities in the USA). We ignore some small, mostly island nations (see the Caribbean image below) but will include a general admin_0 polygon for the entire country instead. First order administrative units are composed what most people call “provinces” and “states” (not to be confused with countries aka “states”). For some countries, we will also include 1st order admin “regions” that group smaller 1st order units into larger statistical areas (eg: the United Kingdom’s England, Scotland, Wales, and Northern Ireland).