Noll’s New Official Guide Map of Philadelphia, 1897

The colored areas in the northwest section of the city indicate drainage areas to the Schuykill Intercepting Sewer, which ran along the east bank of the river to collect sewage that would have otherwise flowed into the river and polluted the water supply above the Queen Lane, Belmont, Spring Garden, and Fairmount pumping station intakes. The numbers probably indicate the area in acres of each drainage area.