Most grid systems don't have overlapping squares because they are quad trees. Each point identifies a single rectangle they are in, and all the parent rectangle

Most grid systems don't have overlapping squares because they are quad trees. Each point identifies a single rectangle they are in, and all the parent rectangles that fully contain that rectangle. H3 doesn't have that property between levels. Cells at a level don't overlap. But the the seven children of a cell might overlap with neighboring parent cells. Of course rectangles aren't rectangular when projected on a sphere. Because there are no straight lines. Rectangles and hexagons are 2d shapes that are applied to the 2d projections of spheres. They only look like rectangles or hexagons in 2D.