Thanks to this world map that shows the density of people with the surname Westerman in different countries, you can get an idea not only of the popularity of the surname Westerman in each country but also of the different migrations of people surnamed Westerman.
The quantity of people with the surname Westerman that we can find in each country can help us discern the origin of the surname Westerman, as logic tells us that the place with the most people surnamed Westerman will be the country or area of origin of the surname Westerman.