A basic sprinkler in Stardew Valley waters the four orthogonally adjacent plots. Space and walking time are somewhat limited, so you want to optimize for that.
Looking at those outputs is a little confusing since not all dots will actually be watered. The partitioning also adds to that.
I was assuming the OP was talking about iridium (or at least quality) sprinklers, the graphs don't look like good placements for basic sprinklers at all. I guess basic sprinklers do pose a somewhat more interesting problem - then again you use them only for a very short time before moving on...
Now if it included scarecrow placement and shortest distance for non-traversable crops like beans, that would be something else...
Looking at those outputs is a little confusing since not all dots will actually be watered. The partitioning also adds to that.