A town plan is three things laid down at different times and lasting differently long: the streets, the plots, and the buildings on the plots (M. R. G. Conzen, 1960). So a city is a palimpsest. Drag the year, or play it.
Grown by polis (the default): first the ground, a heightfield in metres: hills, a river meandering in its floodplain below a terrace scarp, perhaps a coast, no slope steeper than the soil stands. Then polis's settlement field grows a town on it for nine centuries (a land market, lanes, walls, bridges; the town founded and spreading where the ground allows). Then morph reads the field: each built cell is laid out in the plan of the era it was first built in (the walled town an organic core inside its ring; later Georgian grids, boulevard schemes, suburbs, modern grids), the field's busiest lanes run on through every plan as old roads while a grid erases the field paths, blocks are cut back to the river's banks (quays), the field's bridges cross it when the field built them, and land value is the field's rent. Too steep to build is a park; every building is levelled on the ground. It takes the field several seconds to grow. Sketch is the quick synthetic town on a flat frame.
The countryside comes first: lanes out of a market town, and hamlets on them. Every later plan inherits both. A lane is never erased: it runs on through the grids as an old road (Broadway through Manhattan), and a hamlet survives inside the city as an urban village, its own small cell that the later plans flow round.
Districts are grains: each was laid out in one era by one idea of a street (an organic core, a planned grid, a boulevard scheme round a rond-point, a suburb, a modern grid), each at its own angle, so where two meet the blocks are cut short. The old core's edge is where its wall stood: a ring boulevard. A block too small to build on is absorbed by its neighbour (the street between them closes), or left as an island or a pocket square.
The fabric is a field: land value falls from the core and rises on the big streets, and heights follow it. An unplanned district's plots and heights lean toward its neighbour's over the seam, as growth does; a planned one keeps its edge.
Buildings have histories. Each plot is built in its plan's style, then waves of redevelopment (1780, 1870, 1965, 2005) rebuild where the land has come to be worth far more than what stands on it: often on the big streets, rarely on quiet ones, so old houses survive where values stayed low. A rebuilding often takes its neighbours' plots too, so a modern slab stands on what were six medieval strips. Tap a building for its plot's history.
Plan: drag to pan, wheel or pinch to zoom, tap to inspect. Model: drag to turn, shift-drag or two fingers to pan.