It sounds like you want a Hash of Hashes, that looks something like:

$VAR => {
    City-Center1=> {
        Data-items for first combination  }
    City-Center2=> {
        Data-items for second combination }
...
}
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Where the top-level is keyed by the concatenation of the city and center names and a reference to the hash of the data for each city/center combination is the top-level value. Then your center-within-city becomes a simple sort of the top-level keys, and a dereference from the coresponding value.

In Pseudo-Code (because I haven't run it through the interpreter) --

my %city_center_hash;

# Loading the data structure --
while <DATA> {
   ($variables) = split data line
   my $this_key = "$o_city|$o_tcenter"; # select an
                                        # appropriate
                                        # separater
   $city_center_hash{$this_key} = {
       data_item1 => variable1,
       data_item2 => variable2,
#      ...
       data_itemN => last_variable,
    };
}   
   
# ....
# ....

# Retrieve the data from the data-structure

foreach $cc_combo (sort keys %city_center_hash) {
 
    my ($this_city, $this_center) = split /\|/, $cc_combo;

    my $these_data = $city_center_hash{$cc_combo};

    my $variable_item1 = $these_data -> {data_item1};

    # Do something with the names and the first 
    # data variable
    # etc ....
}
[download]