Perhaps you will want to see the Wikipedia entry on Crime Prevention Through Environmental Design (CPTED).
From that article:
As established by [Oscar] Newman, defensible space must contain two components. First, defensible space should allow people to see and be seen continuously. Ultimately, this diminishes residents' fear because they know that a potential offender can easily be observed, identified, and consequently, apprehended. Second, people must be willing to intervene or report crime when it occurs. By increasing the sense of security in settings where people live and work, it encourages people to take control of the areas and assume a role of ownership. When people feel safe in their neighborhood they are more likely to interact with one another and intervene when crime occurs. These remain central to most implementations of CPTED as of 2004.
It should be noted that most criminals seem to understand this perfectly well. Quite frequently, immediately before a neighborhood is "captured by crime", a few "alpha criminals" engage in a pattern of activity which seems almost intelligently designed to discourage non-criminal residents from being out in their yards or in the streets.
If criminals can drive the non-criminal community inside, through acts of violence or near-terrorism, this effectively leaves the streets ceded to the criminals, who can thereafter maintain their reign of terror, violence, and crime. If people are afraid to even look out of their windows, criminals have no real fear of being observed in illegal acts. Indeed, if they can force even a bare majority of citizens to huddle inside and isolate themselves from the community, they can focus their terroristic violence or predation on those who dare to try to observe and report them. This carries the message to those who have been isolating themselves that they are taking the proper course, and that getting involved is effectively choosing a course towards suicide.
Few things are better for a community, in terms of reversing a condition of ubiquitous isolation from the community, than a good old-fashioned National Night Out Against Crime. Additionally, it is useful to gain the assistance of police and form a Neighborhood Watch.