How to read a Maps rank grid: average rank, coverage and top-3 share

Short answer: look at three numbers together. Average rank shows how high you appear where you show up. Coverage shows how much of the area you show up in at all. Top-3 share shows how much of the area you'd actually win calls from.

The three numbers

Metric	How it's worked out	What it tells you
Average rank	The mean position across the grid points where the business was found	How strong you are where you're visible. It can look great even if you only appear in two spots.
Coverage	Points where you were found ÷ total points	How much of the service area can see you at all.
Top-3 share	Points where you ranked 1-3 ÷ total points	Roughly how much of the area you're likely to win clicks and calls from.

A worked example

On a 3×3 grid a business ranks 1, 2 and 2 at the three points nearest its office, 8 and 12 at two more, and isn't found at the other four. Average rank is (1+2+2+8+12) ÷ 5 = 5.0. Coverage is 5 of 9 (56%). Top-3 share is 3 of 9 (33%). The average sounds fine. The other two numbers show that half the area can't find the business.

What to do with it

High average, low coverage: you're strong close to home. Work on relevance for the outer areas, for example service-area pages that mention the neighbourhoods you serve.
Good coverage, few top-3 spots: you're visible but not winning. Look at review count and freshness, your primary category and how complete your profile is, compared with the businesses above you.
Scores moving between scans: compare like with like, using the same centre, grid size, radius and phrase (see choosing grid size and radius).