The science
The same solver as the 3D table, drawn from above. Heights are shaded as a hillshade with the sun in the north-west and 10 m contour lines. Water uses the depth-averaged shallow-water equations ∂h/∂t + ∇·q = 0, ∂q/∂t + ∇·(qq/h) = -g h ∇(h+z) - friction on a 256 x 256 grid with 10 m cells. Erosion follows a stream-power law with sediment capacity C = K sin(a) |u|; steep slopes slump (thermal erosion); lava is a Bingham fluid that stops where the yield stress exceeds the driving stress. Villagers walk with Tobler's hiking function and A* paths.
Honest limits: weather, erosion, cooling and the villager clock are cartoon-scaled with labelled accelerators; no turbulence, no bank collapse, no infiltration. Buildings are drawn larger than life.
Independent checks (button below) compare the solver with the analytic Ritter dam break, the stream-power slope-area law, the Bingham stopping thickness, A* vs Dijkstra, and the mass ledgers.