I know that local Google map listings are partly dependent on proximity and citations. My site consistently ranks on page one for city specific key words, but it only shows up on the local map if the city is within about 15 miles of my GMB listing. However, my competitors (that I typically outrank in the SERPs) are often 20-30 miles further away and still show up on the local map.
I'm wondering what other factors determine might impact why my competitors show up when I do not. I'm guessing that SERP ranking isn't directly tied to local map listings though.