Every watered lawn in Nassau has a second map underneath it: pipe runs, valve boxes tucked into the mulch, splices in a waterproof cap, a sensor up on the eave waiting for rain. Jimmy's Lawn Sprinkler Services, Inc. reads that map for a living. Spring is start-up season — lines charged, heads checked one at a time, arcs walked back off the driveway, a controller set to what the yard actually needs. When something fails mid-summer it is usually small and buried, and finding it is the craft: a soggy patch, a weak zone, a head mowed flat years ago. Before the ground locks up they blow the water out, and the system waits underground for the next April.