It looks almost like an average-size house that's been sliced in half. At 12 feet wide, the neat, new single-family home is squeezed onto the slenderest of strips of land on a Brooklyn Park street of modest, post-World War II houses. The home joins an 18-foot-wide one built in the past year in the community that spans Anne Arundel County and Baltimore City. A similar house is planned for another of the 25-foot-wide empty lots in the area. While building on these infill lots in mature, developed communities with established roads, sidewalks and other infrastructure is considered "smart growth," residents...