my %data = {
   'CityA'=>{
      'PopByAge/Gender'=>{
         'Ages 0-9'=>{
            'Male' => 220,
            'Female' => 180
         },
         ...
      },
      'FamilyHouseholds'=>{
        ...
      },
   },
   ...
};

##</code><code>##

print "What city? Choices are:\n", 
      join(", ", sort keys %data), "\n>";
chomp($city = <>);
my $hr = $data{$city};

print "What table? Choices are:\n",
      join(", ", sort keys %{$hr->{$city}}), "\n>";
chomp($table = <>);
$hr = $hr->{$table};

print "Which group? Choices are:\n",
      join(", ", sort keys %{$hr->{$table}), "\n>";
chomp($grp = <>);
$hr = $hr->{$grp};
...

##</code><code>##

# Each city may have different tables, so trawl through all the
# cities to find available table names
my %tables;
for my $city (keys %data) {
   $tables{$_}{$city}=$data{$k}{$_} for keys $data{$k};
}
print "Which table? Choices are:\n",
   join(", ", sort keys %tables), ">\n";
chomp($table=<>);

print "Which city? Choices are:\n",
   join(", ", sort keys %{$tables{$table}}), ">\n";
chomp($city=<>);
...

##</code><code>##

my %data = {
   'PopByAge/Gender'=>{
      'Ages 0-9'=>{
         'Male'=>{
            'CityA'=>220,
            'CityB'=>...
         }
      }
   },
   ...
};

##</code><code>##

my %data = {
   'Cities'=>{
      'CityA'=>{
         'PopByAge/Gender'=>{
            'Ages 0-9'=>{'Male' = 220,'Female' = 180},
            ...
      },...
    },
    'Tables'=>{
       'PopByAge/Gender'=>{
          'Ages 0-9'=>{
             'CityA'=>{'Make'=>220, 'Female'=>180},
             ...
    ...
};

##</code><code>##

my @data = [
   { city=>'CityA', table=>'PopByAge/Gender', 
     grpA=>'Age Group', grpB=>'Gender', A=>'0-9', B=>'Male', val=>220 },
   ...
];

##</code><code>##

my @selected = ( @data );
while (1) {
   print "Search by city, table or group? (or D for done)";
   chomp($key=<>);
   last if $key eq 'D';
   my @choices = map { $_->{$key} } @data;
   print "Choices are: ", join(", ", sort @choices), "\n>";
}
... print report on selected data ...