If you are using at least Perl 5.10, the Module::Load module should be in core. It would allow an implementation something like this:

# Arguments are city code ('lon' or 'par') and an environment ('prod' 
+or
# 'test')
use Module::Load qw{ load };
sub load_database_module {
    my ( $city, $envir ) = @_;
    state $city_map = {
        lon    => 'London',
        par    => 'Paris',
    };
    state $envir_map = {
        prod    => 'Production',
        test    => 'Test',
    };
    state $type_map = [ qw{ Prod` Test } ];
    $city_map->{$city}
        or die "Invalid city '$city'";
    $envir_map->{$envir}
        or die "Invalid envir '$envir'";
    my $class = sprintf 'App::%s::%s::LogTable', $city_map->{$city},
        $envir_map->{$envir};
    load( $class );
    return $class;
}
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