there is a sexual interpretation of the relationship between the two individuals. the area had an estimated population of 4 500 000 in 2010, spread over a combined area of . therefore, given a point with code a on the water system, a point with code b is downstream if:

 the first exactly n digits of each code match, where n ≥ 0, and
 the remaining digits of b are:
 less than the remaining digits of a, and
 all odd. a similar result was shown when looking at pairs of friends and strangers. the girls soon see the couple's boat approaching them. 