I think he has been doing it that way close to 20 years. The intent is to look at the lines and project based on what lines u are between and/or near.
But you are right, those gaps can get pretty tight in some areas, plus he goes from <1 straight to 3 in this case. So if you are 20 miles east of the 3” line, no clue if he is thinking “almost 3” or “under 1”. Then you hit the 6” line 30 miles the other way
Plus it doesn’t account for local climo factors. Much better ways to present it these days.