my @key1_order = qw/AB PL B/;
...
foreach my $key1 ( @key1_order ) {
   ...
}

##</code><code>##

$coord_{AB}{order} = 1;
$coord_{PL}{order} = 2;
$coord_{B}{order} = 3;
...
foreach my $key1 ( sort { $coord_{$a}{order} <=> $coord_{$b}{order} } keys %coord_ ) {
   ...
}