Fen-edge district Voronoi overlay

Clean rebuild: Downham → North Witchford → Ely → Whittlesey → Huntingdon → Thorney → Peterborough → Newmarket → Cambridge

Stage Stage 9 parish cells district dissolved surfaces parish points

This is an analytical overlay, not an official boundary map. It uses parish/settlement geocodes where available, supplemented by manual anchors for sparse or difficult fen-edge parishes. Use the parish point layer to spot bad anchors before trusting the dissolved district shape.