Use an anonymous array as value:

$coordinates{$zone} = [ $a1, $a2, $b1, $b2 ];
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Don't forget to dereference it when you read your coordinates back out:

($a1, $a2, $b1, $b2) = @{$coordinates{$zone}}
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Have a look at perlref and perlreftut.
Hope this helped.
CombatSquirrel.

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Entropy is the tendency of everything going to hell.