If you need real coordinates, an Array wouldn't be enough. You can switch to a HoH (Hash of hashes), something in the lines of:

my $HoH = { 101.67 => { 80   => 5 } , 
            312    => { 67.8 => 7 } };
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Then you can retrieve the values with $HoH->{312}{67.8}.

Just be aware that hash keys are strings, so use sprintf if you get them from variables, or you're going to get strange results.