Why a single ranking number misleads local businesses
In classic web search, a keyword has roughly one ranking. In Google Maps it does not. Distance between the searcher and the business is a ranking input, so your position changes with the physical location of the person searching. The same query, typed from two streets apart, can return two different orders.
This is why a plain "you rank 4th for plumber" statement is close to meaningless for a local business. Fourth from where? Outside your front door you may be second; three kilometres away you may not appear at all. Both facts are true at the same time, and only one of them affects the customer who is actually searching.
Search Console does not solve this either. Its position metric is an average across every impression — different users, neighbourhoods, devices and histories collapsed into one figure. For broad organic SEO that average is useful. For Maps it hides exactly the variation you need to act on.
Grid rank tracking exists to expose that variation. Instead of asking "where do I rank", it asks "where do I rank from here, and from here, and from here" — then puts the answers on a map so the pattern becomes visible.