The rules of tennis say, "The stringing pattern must be generally uniform and, in particular, not less dense in the centre than in any other area." If the strings get closer together on the outside you 1-Did not skip a grommet hole you should have skipped, or 2-You strung too many mains.
Most 16 main rackets skip either 7&9 or 8 at the head and or throat. Most 18 main rackets skip either 8&10 or 9 at the head or throat.
Tie off locations are deformed by knots and the mains bend the grommets up and down the racket where cross bend the grommets across the racket.
Just looking at a racket most of the time you can tell how it should be strung especially if it is strung or has been strung correctly before.
I hope I am not coming across as condescending to anyone. But try looking for these signs all the time and you will find you need patterns less and less. More often than not the pattern 16x19 and tension range is written on the racket and many rackets have tie off holes and skipped holes marked in some fashion or another.
I would like to apologize to anyone I have not offended. Please be patient I will get to you shortly.