15-Minute City Isochrone Contour Map (2D)

The same 15-minute-city planning model, viewed the way a real isochrone map actually looks: instead of orbiting a coloured 3D block city, this version extracts true equal-walk-time contour lines from the exact Manhattan-distance time field using the marching-squares algorithm, the standard technique for turning a sampled scalar field into topographic-style isolines. A histogram beneath the map shows the live distribution of walk times across every block that already has all four essential amenity types, with the current target time marked — a statistical readout that a rotating 3D scene has no natural place to show. Place schools, groceries, parks and clinics on the same street grid, tune walking speed, block size and the target time N, and watch both the contour shape and the histogram respond instantly.