The inspiration for this catscape was three-fold:
Before Arlo & Boris came along, Annabelle had the place to herself and would frequently jump up onto the narrow window sill to watch the deer, squirrels, birds, and other cats that wander along that side of the house. Once Arlo saw how Annie used the window sill, he claimed it for himself. Annie is also a little older now, so the jump is a little more difficult for her. Therefore, I wanted to create a path that would ascend to the window sill gradually and that would provide multiple levels for looking out. Frequently, I strive to obscure hierarchies by constructing an optimal viewing spot that is NOT the highest position on the catscape.
Given how much Annabelle and Arlo like to sit at the window sill, it made sense to make it a wider platform for them there.
Boris has a lot of fur between his toes, so he never even tried to get up to the window sill, which is slippery as well as narrow. But I could see he was jealous of his siblings having access to that vantage point. So the sloping approach up to and down from the window allows him to participate in the fun.