my @records;
while (<IN>) {
    # Write a parse_record subroutine to return the variables you want
    my ($NUM, $SEC, $LONG, $LAT) = parse_record($_);

    # Stick your variables into an array for later use
    push @records, [ $NUM, $SEC, $LONG, $LAT ];
}

##</code><code>##

# Sort by LONG (index 0=NUM, 1=SEC, 2=LONG, 3=LAT)
my @sorted_recs = sort { $$records[$a][2] <=> $$records[$b][2] } @records;

##</code><code>##

for my $rec (@sorted_recs) {
   # pull the variables from the current record
   my ($NUM, $SEC, $LONG, $LAT) = @$rec;

   print "Num=$NUM, Sec=$SEC, Long=$LONG, Lat=$LAT\n";
}