How about a hash of arrays!

eg. $hash{amsterdam} = [23, 88]; etc.

You can generate that from your file using:

#! perl -w
use strict;

my %data; # Choose a better name

#open DATA, '<yourfile' or die "Couldn't open $DATA; $!";

while(<DATA>) {
    chomp;
    my ($place,$number) = split /\s+/;
    push @{$data{$place}}, $number;
}
#close DATA or warn "Couldn't close $DATA: $!";

for my $place  (keys %data) {
    print $place, "\thas values: (";
    print @{$data{$place}}[$_], ',' for (0 .. $#{$data{$place}});
    print ")\n";
}
__DATA__
amsterdam  23
amsterdam  88
london    65
ny      10
ny      16
la      21
la      65
miami     9
lapaz    10
[download]

The program produces this output.

C:\test>193169
miami   has values: (9,)
lapaz   has values: (10,)
ny      has values: (10,16,)
la      has values: (21,65,)
london  has values: (65,)
amsterdam       has values: (23,88,)

C:\test>
[download]

I'll leave cleaning the output up to you:^)