A recent commenter on my posting about 40 Hancock Street noted that Dorchester is dense by suburban standards, but not by urban standards. The irony is that much of Dorchester initially served as a suburban alternative to Boston proper in the late 19th and early 20th centuries. Jones Hill had more density (if we measure density by people per acre) fifty years ago then it has today. The decline in population has been somewhat offset by an increased number of dwelling units with the conversion of some single family homes into apartments or condominium units. One can argue that the neighborhood could become more dense with houses and people, given the decline from historic levels. But density isn't solely about the number of people per acre or the number of dwelling units. Density manifests itself in many other guises: noise, traffic, trash, among other issues. The density of cars has increased, for example. On a hill where offstreet parking is scarce, the conversion of a single family home into three condominium units can double or triple the number of cars associated with the property. The commenter argues that sometimes too much value is placed on having green open space. I would counter by saying that in many cases it isn't the green open space itself that is valued (vacant lots in and of themselves aren't useful and most people prefer parks), it is the absence of yet another structure that people prize.
The debate over density and its concomitant effects should inform how we view infill housing and the effect new construction has on a neighborhood. Out of this debate should come a better set of standards for evaluating the impact of new development at the neighborhood level. The simplest way to preserve the character of a neighborhood is the renovation and rehabilitation of the existing building stock. This won't always be possible and sometimes a building will need to be torn down and replaced or a vacant lot will be built upon. It is in these cases that particular care needs to be taken to understand how the proposed development will affect the life of the neighborhood.