Cool! I'd love to have a look at that, but the two links in the paper seem to be broken :( http://roadlessforest.eu/map.htm and http://www.map.ox.ac.uk/accessibility_to_cities/

This seems to be the article behind the paywall: https://ora.ox.ac.uk/objects/uuid:5c2ebe20-a1c2-44cb-bd71-95...