Natural Surveillance
Seeing and being seen are important aspects of crime prevention. Natural surveillance guides the placement of physical features such as windows, lighting and landscaping which affect how much can be seen. A potential criminal is less likely to attempt a crime if he or she is at risk of being observed. At the same time, we are likely to feel safer when we can see and be seen. (Virginia CPTED Committee, 2002)

Give them something to look at... and they'll look at it! Natural surveillance truly does exist in the human population. Whyte (1980) demonstrated this by extensively studying the behavior of individuals in urban areas using time lapse photography. Whyte observed that people enjoy sitting under trees and watching pedestrians. This provides a great opportunity to combine trees and sitting places (i.e. benches) near strategic public places in need of natural surveillance (i.e. greenways). It is critical that an arborist and landscape designer be involved in the selection and installation (and pruning) of plant material to facilitate the natural surveillance.  

Here are some general guidelines to help you landscape with respect to natural surveillance:

• Plan & plant for clear lines of sight for the following: street-to-site, site-to-site, around the site. This is especially important for residential landscapes since most robberies occur when the residents are not home.
• Attract eyes. Create something spectacular! Give pedestrians and neighbors something to look at, like bulbs in the spring, annuals and perennials during the summer, plants that change colors in the fall and plants that provide food and shelter for birds in the winter. 
• Install swings, benches, and porch/lawn furniture to create an outdoor living area that will  allow for natural surveillance.

Office Building Across from Washington Hilton

Canopy Up or Canopy Down: Which floor gets the view?
Trees, like typical street trees, located in front of buildings usually block the view from one or more floors to the street and sidewalk area directly in front of the building. Natural surveillance will be hampered by the presence of medium and large trees growing in close proximity to buildings. How should trees be pruned to improve natural surveillance in these situations? I recommend crown raising to make sure people on the first (ground) floor have the ability to see the street and sidewalk area. I have two reasons for making this recommendation. First, if an assault or robbery was occurring, individuals on the first floor have a better opportunity to see the assailant (to make a positive identification later) and, more importantly, to intervene and provide assistance to the victim. Second, it is very expensive to repeatedly perform crown reduction and may eventually shorten the life of the tree.  

Video Surveillance
As more communities adopt the use of closed circuit television and webcams, conflicts are sure to occur between the need for maintaining tree canopy coverage and video access. Perhaps the introduction of additional cameras (at lower heights) will allow for the necessary video access while leaving the existing tree canopy coverage intact. Skilled landscape lighting technicians working with a consulting arborist may even elect to install video surveillance equipment in trees. Masking the location of video surveillance helps to decrease target hardening and makes the bad guys unaware their being monitored.

Plant Selection
Large shade trees can help create areas in the landscape where intended users will congregate and provide natural surveillance (porch, gazebo, water garden, etc). Trees come in a variety of shapes and sizes. At one end of the spectrum are excurrent trees, like pine and spruce trees, which consist of one central leader and limbs of decreasing length proceeding up the trunk. At the other end of the spectrum are decurrent trees, like elms, which consist of a number of codominant leaders. Large decurrent trees provide excellent shade and are able to avoid conflicts with the ability of pedestrians to provide natural surveillance since the canopy is elevated. Excurrent trees, on the other hand, work against natural surveillance since the majority of the tree’s canopy is close to the ground blocking the ability of individual’s to perform natural surveillance. Inspect large decurrent trees growing near homes and buildings and have limbs pruned that may provide climbing access to upper story windows/rooftops. [click on the heading for additional information for this topic]

Landscape Lighting 
Lighting improves natural surveillance from dusk to dawn by making an entire space more visible and taking dark zones away. Motion detector lights are particularly effective since they attract natural surveillance when triggered by movement. Good lighting will provide a more secure environment and will encourage more people to use a space after dark. Lighting is the most important security feature in a parking facility (Smith, 1996). The improper use of lighting, including landscape lighting can actual hinder natural surveillance. Uniformity is more important than brightness. It is essential that lighting be uniform, even if the lighting is relatively low, the uniformity of the lighting will allow one to detect the movement of another person. Landscape lighting improves natural surveillance. Effective landscape lighting is particularly important for senior citizens moving around on a site (illuminating steps or uneven terrain). Metal halide allows us to see more of the blue-green spectrum at night and as a result, makes foliage look better.  [click on the heading for additional information for this topic]

No Front Porch?
Retrofit the front yard to create a pseudo-front porch or landscape an area in the front that will serve as an area for family and friends to congregate. 

Designing a commercial landscape?
Take advantage of your free surveillance (smokers). Position the assigned smoking area (i.e. gazebo) so the smokers can watch the parking lot or other sensitive areas.

Sound
At night, or in areas where natural surveillance is not possible, an environment can be created that will generate sound to announce the presence of unwanted visitors. One may construct a bed of pebbles or gravel, instead of mulch, especially under ground-floor windows. Another way to detect the movement of individuals, particularly around corners, is by installing low hanging wind chimes. There are outdoor light-triggered devices that can signal the presence of someone (similar to devices used by stores to announce the entrance of a customer).

Smith, M. 1996. Crime Prevention Through Environmental Design in Parking Facilities. Research In Brief from National Institute of Justice. NCJ157310.

Whyte, W.H. 1980. The Social Life of Small Urban Spaces. New York: Project for Public Spaces.