How are postcode areas worked out?

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Tags

1. #district
2. #represents
3. #postcode
4. #following
5. #letters
6. #premises
7. #digit
8. #system
9. #generally
10. #right
11. #digits
12. #within
13. #first
14. #street
15. #single
16. #letter
17. #working
18. #represent
19. #hierarchical