%hash = map {$_ => undef } qw(city state country);

##</code><code>##

( 'city' => undef, 'state' => undef, 'country' => undef )

##</code><code>##

my %skip = map {$_ => undef } qw(city state country);

foreach my $field (param) {
  next if exists $skip{$field};
  foreach my $value (param($field)) {
     #process non blank thedata variable
     ...
  }
}

##</code><code>##

foreach my $field (param) {
  next if grep { $field eq $_ } qw(city state country);
  foreach my $value (param($field)) {
     #process non blank thedata variable
     ...
  }
}