What caught my eye is e.g. the area just north and south of Elmwood Park, quite deep red but only light blue. Same with the areas surrounding Evergreen Park. In contrast, the near west side (due west of the word "Chicago") has deep blue but light red.
i think that deep blue area is an artifact. i live in that tract, the density of actual in-use service lines is very low due to the urban renewal that clearcut the area.
most residents live in larger buildings and share a small number of water taps. the only part that still resembles a traditional, small lot chicago neighborhood with lots of taps is claremont cottages.