A map I’ve oft looked for over the years is one that depicts a fine-grained measure of density throughout a long period of time. I recently came across SocialExplorer.com through a New York Times feature that credited them. I used the site to make the following maps, all of which are at the same scale:
1940
Our first glimpse of density in the Twin Cities is also the high-water mark, showing the greatest number of census tracts with densities greater than 15k persons per square mile. Note the Village of Morningside gets its own tract but Wayzata and White Bear Lake are merged with their respective counties.
1950
The 1950 census was the zenith of Minneapolis’ population, and it is reflected in this map, with nearly as many high-density tracts as 1940 and significantly higher densities at the edge of the city limits. St Paul, on the other hand, has room to grow (and would reach its own peak population in the 1960 census). This census, however reflects a housing crisis as the market failed to keep up with demand even five years after the war ended and the troops poured home.
1960
The suburbs gained definition and density as the central cities had long since quit annexing their neighbors, presumably preferring to consume themselves with urban renewal. Saint Paul suffered most, as the capital area renewal guts the apartment districts on the north sides of downtown. Renewal in Minneapolis has more subtle effects, but is evident in the drastic decrease in density in the Glenwood area, the city’s first Federal renewal project.
1970
The freeways make their presence known – notice the drop in density in the tracts that follow the route of 35W through South Minneapolis. Rondo disappears here, too. The 60s are famous for their turbulence, and the Plymouth riots are present on this map in the disappearance from the North Side of the last two tracts with densities over 15k. The reason I keep mentioning that level of density is that it is often considered the threshold for rapid transit, which would be considered and ignored in the 70s, even with the densities shown here that are much higher than today’s.
1980
It’s hard to find good news in the 1980s census, but if we ignore the dispersing sprawl we can focus on the urban renewal housing projects such as Riverside Plaza and the Gateway Towers, which are likely responsible for density jumps in their respective tracts.
1990
Ouch. Moving on…
2000
Ah, that’s better. 2000 shows a significant increase in inner-city density, often attributed to increases in immigration.
2007 (estimate)
Which makes me think this estimate is low. Certainly immigration has subsided since the 90s, but at the same time multifamily residential has been built at levels not seen since the 60s or 70s. The Mill District is still blank on this map, ignoring the thousands of new residents of that neighborhood.
Currently listening to: “She’s Too Much for My Mirror” by Captain Beefheart
Getting Around Minneapolis 
These are really interesting maps. Is there any way to put them together interactively? It would be cool to be able to see the changes animated. At the very least, you could create an animated gif with off-the-shelf freeware, and then put that up. That way, readers could see how population flowed and changed across the region a bit more easily. (Take a look at http://gickr.com/).