Isn't that amazing? In a city roughly evenly divided between these three groups, just about every inch of the city is overwhelmingly dominated by one group, usually to the exclusion of the other groups. Look at how each area is precisely delineated. These are lines that any South Sider knows instinctively and thinks of almost like a physical boundaries.
Anyways, go play around on the Census Bureau's website, and you'll never be satisfied with the MLA's mapping tools again, even if they do monopolize mappable language data.