Jacobs opens her book with a discussion of a neighborhood in north Boston (in the 1950s/1960s, when she was writing). The area is a slum--only, it isn't a slum. The streets are vibrant and the place has lower crime than many other neighborhoods in Boston. Why then does it still have a reputation as a slum among city planners? She closes her book with a description of a beach area in New York. The beach isn't that great looking, but it does feature clay soil that dries and leaves odd looking "sculpture" one can take home as a souvenir. The beach is next to a park that features grass fields and playgrounds. In the name of improving the area, the city removes the beach, puts in a seawall, and extends the grassy area. What little character the park had is now gone; it's like most other parks. These are the problems, Jacobs notes, with city planning. They are based on theories about cities that are rooted in philosophical ideas that have nothing to do with what actually makes cities work. Jacobs is about to rewrite what city planners should be focusing on.
The theories the Jacobs takes down are those of the Garden City and the Radiant City by Lewis Mumford and Le Corbusier. One felt that cities needed lots of green space and to be less dense; the other created an ideal city that existed as lone skyscrapers amid vast parks. Jacobs says that this overidealization of nature kills cities. Parks have a purpose, but parks for parks sake in the midst of cities are city killers.
Jacobs lays out four basic tenets that successful cities or parts of cities follow: (1) an area must serve more than one purpose; (2) blocks must be short; (3) buildings must vary in age; and (4) the population must be sufficiently dense. Taken together, these are the things that can ensure a successful city, a successful city park, a successful neighborhood, and so on.
The reason an area must serve more than one purpose is so that people come and go through the area throughout the day and night. If all the action is at morning and evening rush hour and at noon, the area will otherwise be dead. This action time is not enough to serve many types of businesses, and those it can serve will close up shop at the other times.
Short blocks are important to allow for ease of access and flow. They simultaneously cut down on traffic and increase the use of any given street.
Buildings need to have a variety of ages--and looks--to further diversity of tenants. Older buildings will generally have cheaper rents and thus tenants of that sort who can afford them. If all the buildings in an area are the same age, they all fall apart at the same time. And only the types of businesses and people who can afford a new buildings will be in the area, and eventually only those who can afford old stuff will be in the area. So those shoe repair, wig shops, and dance studios that can't afford high rents won't come to the new-fangled portion of town, and only some high-priced restaurants will sit along the street. As the neighborhood declines, the restaurants will leave, and if any businesses at all do move in, they are likely to be of only one sort (e.g., thrift stores).
Density is important because without it, crowds can't fill the streets and make businesses want to open up or stay open.
Jacobs also covers specific examples of various city structures. She notes how sidewalks are best when they are used frequently and at all times of the day. Her four tenets are the means by which one gets crowded sidewalks. Sidewalks that are in use reduce crime and thus blight, because where there are people, thieves and their ilk are less likely to operate. With neighborhood interaction and personal investment in that neighborhood, children are less likely to act up and are also safe from danger. The same tenets can be applied to parks. They need to be in places where they are used by different kinds of people throughout the day and where there are enough people to fill them. Like sidewalks, this is what makes them safe--and popular.
She also covers material on how parts of a town have a natural inclination to become less diverse with time--and thus less successful as a neighborhood. As a neighborhood becomes more popular, poorer residents and businesses have to move out, and slowly all those wig shops and dance studies are replaced by restaurants and offices. Too many of the latter, and the mix of people and the times of day that are spent in the place becomes more segregated. Nights fall off (or days, if the neighborhood moves in another direction), and soon that popular neighborhood is not so popular anymore. Maintaining the mix of ages of buildings is one way to fight this, as is the city offering financial benefits to certain types of businesses for staying. The point is to keep the area diversified. (On the contrary, cities often tend to do the opposite--putting all the government buildings or art institutions in one sector--which kills the neighborhood via a lack of variety.)
She also covers something she calls "border vacuums." This is where a large piece of infrastructure gets in the way of the neighborhood, essentially killing off things as one nears the point. These could be large parks, railroads, highways, long blocks, stadiums, waterfronts--anything that is big and long and doesn't offer much in the way frequent and all-day foot usage. Instead of placing yet more parkland in such areas (as cities often do), Jacobs says, things that encourage frequent usage should be zoned or placed in these spots.
She covers how to get rid of slums, which seems a particularly difficult problem to solve. For her, it's a matter of encouraging people to feel a sense of community--to stick around in the neighborhood so that they have something at stake in it. Of course, if it's a slum, folks naturally want to move out, so that's the problem. But a typical solution--obliterating the slum and starting from scratch only exacerbates problems. The slum dwellers are moved wholesale to a new area. Any sort of businesses that did manage to get a foot into the slum are closed up. All buildings are of the same age in the new area. And no one feels all that connected to it. Getting rid of a slum is a slow process.
One of the problems with such areas is financing them. Folks can't get credit to build new structures, enhance old ones, or start businesses because of the bad reputation of the area. Jacobs sees various solutions--government guaranteed loans, local loans, neighborhood organizing. In one case in Chicago, a neighborhood banded together to threaten to withdraw what savings they did have from a given bank if credit was not extended. The banding together did the trick.
Finally, Jacobs also covers the problem of cars on city streets. Remove them from the streets, and no one will venture to a given area because it is too hard to access. Put enough streets and parking in to allow for the cars, and the city becomes too spread out and lacks the density necessary to make it thrive. She proposes a counterintuitive solution: making the cars go away through attrition. That is, make them less convenient to use and people will stop using them. One can encourage the right kind of vehicles on certain streets by doing things such as adjusting lights so that constant traffic stops make a given street inconvenient for through motorists but are perfect for frequently stopping buses and maybe for delivery trucks. Provide fewer parking spots to encourage use of public transportation or taxis.
To what extent are Jacobs's ideas real to me? Walking on a street with more people around certainly does feel safer most of the time. But I also think of some areas in the town where I live that would be considered slums. I would not feel safe walking them at night, even though there are lots of folk around. Businesses--what few there are in such areas--are often closed at night or have bars on the windows. How such crowded areas can also feel unsafe I am unsure. Still, by and large, areas that follow her four tenets do seem to be more to my liking, as would be the case of the city centers of all of the cities where I've lived. Downtown Los Angeles was dead at night when I was a kid (primarily office buildings), but my hometown of Pasadena refurbished many of its older buildings on the west side of town and the diverse set of uses that were put down there, along with the number of apartments placed close by, and the short blocks have all made it a very busy and exciting part of town.