Rank grid — measuring local rank at many points across a map rather than at one, because local results change from block to block.
One number is not a local ranking
Local results are shaped by where the person searching is standing. A business can be first at its own address, fourth a mile out, and invisible three suburbs over — all for the same search, at the same moment. A single reported position is an average of a thing that has no meaningful average.
A grid samples the same query at dozens of points across a service area and reports each one. What comes back is a coverage map: where you are the obvious answer, where you are a maybe, and where you do not exist.
What it is honestly good for
Two things. Showing where the business is actually winnable, so budget goes to the parts of the map that can move. And showing change over time, which is the only reliable read on whether the work is doing anything.
What it is not good for is a number to celebrate. Grid averages are easy to flatter by choosing a tighter radius. Ask anyone showing you one what the radius was, and whether it has changed.
Related: local pack, Google Business Profile, share of AI voice.