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my %data = {
   'CityA'=>{
...
   },
   ...
};

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

# Each city may have different tables, so trawl through all the
# cities to find available table names
...
   join(", ", sort keys %{$tables{$table}}), ">\n";
chomp($city=<>);
...

my %data = {
   'PopByAge/Gender'=>{
...
   },
   ...
};

my %data = {
   'Cities'=>{
...
             ...
    ...
};

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

my @selected = ( @data );
while (1) {
...
   print "Choices are: ", join(", ", sort @choices), "\n>";
}
... print report on selected data ...