Level 1-5:  Tourist (top cities only)

Level 6-15:  Provincial Hopper

Level 16-30:  Local Connoisseur

Level 31 & Up:  Born in Vietnam?

Source code for this map is on GitHub.
It was designed and built by Jeff Allen in 2017 (updated in 2022 at the School of Cities) using Mapbox and QGIS, with data from OpenStreetMap and Natural Earth.