I wouldn't take up a lot of memory with a giant hash of every possibility if I could avoid it. Would it be possible to have a smaller hash or array of the zone ranges and some if statements to figure out what zone a given coordinate is in when you need it?

my %zones;
$zones{B1} = [1,23,7,59];
my @this_coord = (5, 7);
my ($x, $y) = @this_coord;
while (my ($zone, $rng) = each %zones) {
  print "Zone is $zone\n" if $$rng[0]<=$x && $$rng[1] >=$x
      && $$rng[2]<=$y && $$rng[3]>=$y;
}
__OUTPUT__
Zone is B1
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