Coding classes in West Sussex

The learner downloads census table WU01UK from Nomis for 21 districts: all seven in West Sussex and fourteen neighbours in East Sussex, Surrey and Hampshire. Between them, 293,311 people commuted from one of these districts to another, and 496,591 worked in the district where they lived. Each district becomes a point in a network, and each pair is joined by a line whose weight is the number of people travelling between them in either direction.

A community-detection algorithm then looks for groups of districts with many more links inside the group than you would expect by chance. The score it tries to raise is called modularity. Two different methods, a greedy one and the Louvain method, found exactly the same four groups, with a modularity of 0.417. Grouping the districts by county instead scores only 0.342: the counties are a worse description of how people actually move.

West Sussex does not appear as one community at all. Its seven districts split three ways: the west joins Portsmouth and the Hampshire border, the north joins Surrey around Crawley, and Adur and Worthing join Brighton. The strongest single links explain why: Arun to Chichester carries 10,551 commuters, Mid Sussex to Crawley 7,119 and Adur to Brighton and Hove 6,615. Crawley is a magnet: 30,706 people from the other 20 districts worked there, more than the 28,828 Crawley residents who worked in their own town.

Learning to code in 2026 gives a West Sussex teenager the means to understand the patterns algorithms find, instead of simply accepting them. The longer argument is in why teenagers should still learn to code in 2026.