Peters Brook runs its thin green line through Somerville, and the yards that back onto it green up first every spring. Andy's Landscaping & Tree Service works those blocks with a mower and a string trimmer and an eye for where the grass thins under a maple. Summer evenings here go gold around seven, and a lawn cut that afternoon holds the light in even rows. Cleanups come in their turn — the rake-out in April, the last of the leaves in November. It is plain work, done to the edge, and the edge is where you can see it.