use warnings;
use strict;
use XML::Twig;

my $twig = XML::Twig->new(
    twig_handlers => { town => \&town },
);
$twig->parsefile('datafile_towns.xml');

sub town {
    my ($twig, $town) = @_;
    if ($town->first_child('location')->first_child_text('mapx') > 300) {
        print $town->first_child('towndata')->first_child_text('townname');
        print "\n";
    }
}

__END__

sometown