The problem with heat maps, like this one, is they end up effectively as maps of population density. To make a heat map informative, consider coloring the map zones proportionately to the population in that area.
Not entirely true in this case. If it were then you'd expect to see more in Europe and Asia than this map shows. In the US it does devolve to a population density map.
You're using baked-in world population distribution information exactly to make that statement.