In the lexicon of real estate and city planning, density refers to a concentration of housing units, people and jobs in a particular area. Urban centers — such as New York and Chicago — are usually high-density locales. In fact, density is an inherent aspect of city life. Despite its compactness, however, San Francisco retains a rare small town quality in many of its districts. This unique neighborhood aspect, as opposed to the anonymity of larger cities' high-rise apartments, is what the City's neighborhood associations have traditionally fought to protect.

Proposed high-density projects typically inspire fears of parking crises and traffic jams, obscured views, spikes in crime, and resulting lower property values. Negative reaction to high-density development in San Francisco is usually extreme, commensurate with the City's exorbitant property values, which makes sense: homeowners here have more invested in their properties than the average American and consequently feel they have more to lose.

However, density is not always a bad concept, even if it has somehow connoted a negative word. In fact, well-planned "smart growth" development could help alleviate San Francisco's affordable housing crisis. High-density living, or compact development, as it is more euphemistically known, offers many benefits. If the development is "mixed-use" — i.e., it contains retail shops and office space, as well as housing units — then residents will likely do more biking or walking, rather than just driving. Besides supporting community retail outlets, residents will also get to know each other better as they come into regular contact, resulting in tighter neighborhood security rather than urban alienation. Smartly planned development also makes use of mass transportation and can accommodate a range of income levels. Best of all, density does not contribute to sprawl and helps to preserve open spaces for everyone.