I suspect that somebody "photoshopped" this, because there are several discrepancies here. The first thing I noticed was that one of the ethnic groups was labeled "black" but in 1950 the much more common expression was "Negro." Then I realized that the date on the top--1950--does not correspond to the Mayor's name--Richard J. Daley. Daley was elected in 1955; Martin Kennelly was mayor in 1950. The northwest area of the map also seems to show O'Hare airport, which was annexed to Chicago sometime in the 1950's. This needs more research to figure out what it really is.
Thanks, Tomcat. I couldn't read all the small print, like the 1976 on lower right. Richard J. was still mayor in '76, so that part makes sense. I assume what was done was to take data from 1950 (probably from the census) and reprint it later, which also includes changing the language (from Negroes to Blacks). Come to think of it, 1976 was the Bicentennial of the American revolution, and there were a lot of events related to US history connected to the celebrations, so reprinting historical maps of Chicago in 1976 makes sense.