What I usually do is something like this (your final solution in the OP):

my %location = map { $_ => $london{$_} } qw(Long Lat Elevation);
[download]

However, if that isn't clean enough for you, you could use prototypes to create a bit of syntactic sugar:

sub extract(\%@) {
  my $h = shift;
  map { $_ => $h->{$_} } @_;
}

# usage
my %location = extract %london, qw(Long Lat Elevation);
my %stats = extract %london, 'Population', 'Area'
[download]