We did this last year (although due to scheduling issues I likely will not be able to do game-by-game updates this season). The more detailed explanation is in last year's thread, but the general principle is that each county in the country is assigned to the 68 NCAA tournament teams by geographic proximity (distance from home arena to geographic center of the county) and then the map consolidates as the games are played (winning team takes losing team's land). Here's the starting map for 2019. Duke has the smallest area by population and third smallest (ahead of only Iona and St. John's) by land area and number of counties - only means there's a lot of land out there for the taking.