Good article. Regarding Milwaukee's duplexes, they are a housing type that seems to have withstood changes in preferences. The first house i bought was a Milwaukee duplex. It made for a great starter home with my downstairs tenant covering 70% of my monthly payment. It was in a neighborhood of similar homes, built in the 1920's with great craftsmanship (hardwood floors, built in walnut cabinets, decorative stain glass features) as well as a full basement and huge third floor attic suitable for conversion to additional living space. All on a beautiful tree-lined street with sidewalks, multiple churches and schools within walking distance, surrounded by other neighborhoods with similar greater than 10000 persons per square mile population densities. Economic and well worth maintaining (and about 5 minutes from downtown). That was my personal experience of the significance of Milwaukee's duplex neighborhoods (the story behind the numbers). I think the duplexes do reflect a lot about the character of the city, including its large historic immigrant population and frugality (with the city being more fiscally sound on some measures than any other major US city).What would be really interesting would be to track the forms of new housing in each of these cities. The dominant forms of new housing in Milwaukee seem to be new 3 to 6 story 50 unit or more apartments, adaptive reuse of historic industrial buildings for 50 unit or more apartment buildings, followed by high rise apartment projects and a scattering of other types.