Riverdale falls toward the Hudson in terraces, and every lawn on those slopes carries its own weather — sun on one side of the hill, deep shade under the old oaks on the other, river light coming up silver all afternoon. Allstate Sprinkler Corp. tends the grass along these streets with mowing, edging, trimming and the seasonal cleanups that keep a sloped yard from going ragged. Cutting on a grade is its own skill: the stripes have to hold their line where the ground will not. By June the reward is plain — even green from the retaining wall to the curb, borders cut clean around every bed. Down below the river keeps moving, and the yard above it looks looked-after.