In "The death and life of Great American cities," Jane makes a definitive statement on American cities: what makes them safe, how they function, and why all too many official attempts at saving them have failed. Jane goes on to describes the relationship between the built environment and the behavior of people in the streets resembling the scene of a ballet, like a form of symbiotic relationship between an organism and it's host - a kind of co-dependence.
Jane Jacobs's ideas might be viewed by most as idealistic, but over the past thirty years they have been the foundation of present day cities. Through her intellectual analysis of cities on a whole Jane has put a wrench into conventional thinking on the structure of cities and has helped reshape urban planning. Her ideas has lead us to think about each element of city-sidewalks, parks, neighborhoods, government, and economy as a synergistic unit both encompassing structure and going beyond it to the functioning dynamics of our habitats. Through the empirical analysis presented regarding the problems of modern urban centers, artificially engineered (by architects and urban planners) to meet political and economic agendas, Jane provides a greater understanding of the intrinsic nature of our cities-as they should be.
Jane defines primary uses as those, which bring people to a specific place because they are anchorages. For example offices, factories, dwellings, and certain places of entertainment, education and recreation are primary uses. Including museums, libraries and some galleries. This refers to specific types of businesses only.
The importance of primary uses is that it serves the function of being economically stimulating and fertile environment for secondary diversity (i.e.: enterprises that grow in response to the presence of primary uses, to serve people) if combined effectively with another primary use that brings people in and out and puts them on the street. The importance of primary uses is that it's an effective way of attracting people, it generates diversity.
Jane Jacobs believes that the district must mingle buildings that vary in age and conditions including a good proportion of old ones because it adds diversity to the city landscape. There is a need for old construction among the new one because they are part of a total attraction and total environment that is economically too limited and therefore functionally too limited to be lively, interesting and convenient. When there is diversity in a city, that will most likely entail high-yield, middling-yield, low-yield or no yield enterprises. One can also experience or achieve (economic necessity) low or uneconomic costs, safety in the public and neighborhood streets, convenient and overall personal quality are successful elements of old buildings. A depreciated building requires less income than one, which has not yet paid off its capital costs, and it brings in small businesses. A lack of old buildings is unappealing and not economically feasible, there is a strong correlation between the age of buildings and their usefulness or desirability, stability, diversity in residential populations and enterprises.
Mixed land use areas have their benefits and their downfalls, basically because when a city or a buildings goes up architects don't take into account the unpredictable behavior of people towards built structures or landscapes. If a neighborhood is built and in the middle of it is a bar, arcade, clubs and a few convenience stores then it could attract any sorts of strangers and with enterprises such as these we have to assume it will be the wrong crowd which could be unsafe for not only the good stranger but the residents too and the overall esthetic value of the neighborhood. Mixed land uses brings in diversity and it can make things more efficient and convenient for residents. It can also make the streets safe as Jane Jacobs defines it, because of the people it attracts which keeps it busy, active and quite populated where there are always eyes upon the street belonging to "natural proprietors" of the street. A good example of a mixed land use area is one that has parks, baseball diamonds, ice rink and other recreational attractions, grocery and convenience stores, and maybe employment and for sure a residential mall in the center of the neighborhood. In this way the streets are always lively, livable, and active all year round; it will bring children on the streets and people will enjoy going out for all the right reasons. Moreover, there will always be eyes on the streets of its natural proprietors which will not only bring safety to the neighborhood but strong relationships will develop within the community.
"The continuity of this movement (which gives the street its safety) depends on an economic foundation of basic mixed uses We support these things together by unconsciously cooperating economically. If the neighborhood were to loose the industries, it would be a disaster for us residents. Many enterprises, unable to exist on residential trade by itself, would disappear or if the industries were to lose us residents, enterprises unable to exists on the working people by themselves would disappear." ( Jane Jacobs, pg. 153)
Mixed land use areas are usually more appealing compare to the poor visual scenes in urban landscapes that is often chaotic and sometimes too monotonous. Spatial arrangements of buildings, gardens, enterprises and lights can provide residences with richer (aesthetic) experiences and make the neighborhood more livable and safe providing optimal levels of information.
". that the sight of people attracts still other people is something that city planners and city architectural designers seem to find incomprehensible. They operate on the premise that city people seek the sight of emptiness, obvious order and quiet. Nothing could be less true. People's love of watching activity and other people is constantly evident in cities everywhere. Pg. 37
People are attracted to diversity and overall physical quality of their environment and shift their way around neighborhoods according to the visual information around them.
Jane looks at the character of commercial activity of street, main business of commerce changes over time and how the character of visitor's (strangers') activity as well as residents activity changes.
In summary of Jane's observations, it's the positive effects of people's existence that invites other people, and thus provides liveliness and safe feeling in urban public places; and at night this safe feeling is caused by the differences in light conditions on indoor and outdoor illuminations and the presence of people. Preferred distance and the number of people depended on the physical feature and arrangement of the seating place in public spaces. Overall, architecture, landscape and the built environment influences the shaping of physical space as well as governing and ordering people's perception of it.
Jane Jacobs (1961) The Death and Life of Great American Cities. (New York: Random House): Pg. 29-54, 143-151, 152-177, 187-199.