Urban Edge Externalities

An externality is defined by the Oxford Dictionary of Geography as "A side-effect on others following from the actions of an individual or group. This effect is not bought by those affected and may be unwished for. Thus, while the acquisition of a car may benefit one household by improving mobility, it generates pollution and creates congestion for others.
Externalities may be positive—the building of a hall of residence may bring new business to a local shop—or negative—a new road scheme may create planning blight for home owners. Two types of externality are recognized: public behaviour externalities covering property, maintenance, crime, and public behaviour, and status externalities resulting from the social and ethnic standing of the household."  Read more: http://www.answers.com/topic/externality#ixzz2QJKhSlNW

What are the externalities seen here.  A group of young men use the back of an abandoned house to take a smoke of some weed.  During the week and on weekends young men from all over the community congregate here to smoke and to gamble.  Apart form the potential dangerous climate for neighbours as these men and be scoping out homes for larceny, the garbage left (picture 2 and in the fore-ground picture 1) provides a breading ground for rats and other carriers