When I was studying architecture at Stanford in the late 1950s, one of my teachers was an enthusiastic proponent of redevelopment law, which was then very new. We studied about two projects being planned in San Francisco: Diamond Heights and the Western Addition.
Diamond Heights was an undeveloped area of steep ravines and ridges south of Twin Peaks and Noe Valey. The land had been divided into hundreds of lots along unbuilt streets laid out on paper in a gridiron plan which matched the built parts of the city to the north. The terrain was so steep that the streets could not be built, suggesting that the engineers making the plan had never actually seen the site. Apparently neither had many of the owners, because the lots had been sold to hundreds of different people. Redevelopment law allowed the city to condemn and purchase the lots so they could be re-platted on a street pattern which followed natural topography. From an architecture and urbanistic standpoint the results are banal to say the least: this is not a part of the city that gets featured on postcards or in movies. One is reminded, again, of how depressing much post-war "modernism" was. However, redevelopment gave the city the legal means to correct the planning errors of an earlier generation, and unlike most redevelopment projects no one was dislocated except the wild creatures that had lived there.
Western Addition was another matter. This area, west of Van Ness and roughly aligned along Geary had survived the fire which consumed most of downtown San Francisco after the 1906 earthquake. It consisted of tall Victorian row houses in decrepit condition and largely occupied by very poor and often minority families. When some of us students demurred that the architecture was interesting, our teacher rebuked us with stories of rats, filth, etc. Soon after the land was cleared, but, except for the widening of Geary to expressway dimensions, the old street grid was retained. Some good low income (and low rise) housing was built and a lot of awful projects as well. Two non-residential projects stand out, the cathedral and the Japan Center. Neither is great architecture (My cousin always referred to the cathedral as "Holy Maytag") but they both fill a need. The entire area forever lost the qualities that make so many San Francisco neighborhoods appealing. I can't help but wonder what would have happened if it had been left as is. I suspect that as the enthusiasm for "modern" declined, the Victorians would have found buyers, and the area would have gentrified like so many other parts of the city, ultimately, of course, at the expense of the poor and minorities but not so abruptly.
In my last year another professor assigned us a studio project to plan the redevelopment of South Park in the south of Market neighborhood of San Francisco. He was not a redevelopment enthusiast, but the department chair wanted us to study redevelopment again, so we did. The site was a mixture of light industry and decayed housing, built post earthquake and not picturesque, surrounding a long and narrow oval park, I am sorry to say that no one in the class retained the park or anything else. As I recall, my design was a cluster of factory buildings (one story) with curving concrete slab roofs so popular at the time. Fortunately, South Park was not redeveloped to my plan or anyone else's. The park is still there, surrounded by a quite nice mix of housing, restaurants, and professional offices, with new interesting architecture and old renovated buildings.