Salmon Brook slips through south Nashua behind the neighborhoods, and the yards along it hold their moisture well into a June morning. Berry Brothers Landscaping mows and trims that side of the city on a weekly rhythm, edges the beds and walks, and hauls the leaves away when the oaks finally quit in November. Winter flips the route: plows on the same streets, drives opened wide enough to turn a car around, steps and paths shoveled down to solid footing. Nashua anchors the map, with Hudson, Pelham, Litchfield and Merrimack close by. There's a particular pleasure in the first pass down a street after a storm, headlights on, everything still untouched.