Postman Pat Psychogeographix: Postal Route Calculation on the Fly

Click to enlarge, the red trail is for the three rounds combined as described below, the orange trail is a normal round shown for comparison. Grey lines mark individual postal code/rounds.

A London cabbie has the Knowledge, the postal worker has the Map.    

The post, as I collect it from the depot, is sorted in such a way that it creates a rational, time-economic path that ends where it began and wastes as little time as possible on being between destinations. At the same time each round is identical to the first letter of the postal code. That is pretty nicely organized.

As it happens, for reasons of austerity, several smaller depots in Whiteladies have been brought together into one mega-depot. This means that to cut costs we are now forced to spend more unnecessary time travelling back and forth between depot and streets. My old depot is in the same street as the new one but two blocks further to the end of the street. One of my rounds includes the street the depot is on. The post itself however is still sorted according to the old situation, and this means that you either have to walk a few (hundred) meters extra to reach the starting point of your round or it means that you rearrange your post yourself to accommodate the post to the new situation. The experienced postal worker builds up unique mental maps of the streets s/he works in and to me one of the pleasures of the job is to use this map to recalculate my rounds to make them efficient again. My Garden Village rounds are adjacent and when there is not that much post there is a neat way to combine them into one coagulated route. A mash-up route for which I feel a certain pride. Even though I have been doing this round for ages I can still spent the entire shift going over the route, rearranging it inside my mind to see how they can be recombined into an even more graceful and optimal route. To my great wonder however I have noticed that my colleagues don't share my zest for autonomous route recalculation and will without hesitation walk the same street twice and cross enormous distances to make up for the distorted arrangement between sorting and territory. Bewildering and incongruently they miss out on what makes this job great. 

When I was asked to add an extra round to my Garden Village routine it provided me with an excellent travelling salesman problem on postal scale: how to connect this extra route and how to do it efficiently. The volume of mail for these three rounds combined was such that I could never take it all with me in one go. The extra round could only be connected at one position to my other routes. I could have combined the extra round with the middle round (see pic) and walk the remaining one as normal. A solution that lacks all art and balance. Instead I evened out the three rounds by dividing them up in two new routes to ensure minimal dead-end walking. The result was a breeze with two new rounds of even length. All this on the first tropical day of the year, 8.6km in total. I don't think a land surveyor with a Harvard degree and all the sat nav software in the world could have done better.