Start with the instrument, not the map. In 1859 the engineer Ildefons Cerdà drew a square block 113.3 m a side, cut its corners at 45° and spaced the blocks with 20 m streets and 30 m and 60 m avenues. The corner cut, the xamfrà, is the quiet genius: without it, four buildings meet each crossing at a tight right angle; with it, every intersection opens into an octagon.

It served hygiene and equality after the cholera-era walled city: buildings on only two sides of each block, 16 m high, gardens inside so every dwelling got sun and cross-ventilation. From the 1870s speculators closed the blocks and added storeys. The density assumption failed. The grid held.

Three inputs, one pitch

Read as a system, the plan has three inputs — block b = 113.3 m, street s = 20 m, a 45° corner cut — and one pitch, p = b + s = 133.3 m. Three pitches make the roughly 400 m cell on which Salvador Rueda, director of the Urban Ecology Agency of Barcelona (BCNecologia), built the superilla, the superblock: through-traffic moves to the perimeter, and inside, vehicles enter at 10 km/h and cannot cross. Pilots followed in Poblenou (2016), Sant Antoni and Horta.

The Superilla Barcelona plan (target 2030) reads the rhythm a second way: one street in three becomes a green axis, an eix verd, and where two axes cross, the chamfered octagon becomes one of 21 new squares. According to Barcelona City Council, that yields 33.4 ha of pedestrian-priority space, with every Eixample resident within 200 m of a green street or square. The competition-winning Consell de Cent axis, about 86,000 m², was designed by B67 Palomeras Arquitectos with Cierto Estudio. Rueda wrote the rule; they designed the street it became.

←TODAY: Barcelona is turning one in three Eixample streets into green axes on an 1859 block module.
→3012: Zurich 3012 inherits its streets as rule sets each generation adjusts, not redraws.
Fulcrum: A grid outlives its first programme only if its geometry leaves slack; Cerdà’s chamfer is the slack.

What was measured

The Barcelona Public Health Agency (ASPB) measured the pilots in its three-year Salut als Carrers evaluation (BMC Public Health, 2025). In Sant Antoni, NO₂ fell 25% (a mean drop of 14.6 µg/m³) and PM10 17%, both statistically significant, while car use fell about 20%. Horta, already low in pollution, showed no significant overall change; residents of all three pilots reported better well-being, sleep and social contact. Modelling the full network, Natalie Mueller, David Rojas-Rueda, Haneen Khreis, Mark Nieuwenhuijsen et al. at ISGlobal found that all 503 potential superblocks could prevent 667 premature deaths a year, 117 of them through lower heat alone. From the late 2070s, that is the figure I would underline: street trees cool without drawing on any grid.

Maintenance rose by about EUR 1.07 million in the first year, for cleaning and greenery: a green axis moves cost out of residents’ lungs and into a budget the council must vote every year. That line item is people: the cleaners and gardeners who keep an axis a garden rather than asphalt with planters. Consell de Cent also faces a procedural challenge: in March 2025 the Catalan high court (TSJC) upheld a ruling against the city in a split decision, and the city has appealed in cassation.

Atelier: A Zürich studio entering a street-space Wettbewerb faces Barcelona’s fabric: fixed blocks, fixed façades, one variable left — how the street is used. AI variants are only checkable when the model is fed parameters, not photographs, so the rule set becomes the brief. Monday move: have one person rebuild the perimeter’s block, street and corner rules as a Grasshopper definition before anyone opens a rendering tool.

Hack: Rebuild Cerdà’s 3 × 3 cell as one GhPython component in Grasshopper, with a number slider on input x as the chamfer leg in metres; output a returns nine chamfered blocks at the 133.3 m pitch.

import Rhino.Geometry as rg
b, s, c = 113.3, 20.0, x   # block, street, chamfer leg (m)
ring = [(c,0),(b-c,0),(b,c),(b,b-c),(b-c,b),(c,b),(0,b-c),(0,c),(c,0)]
a = [rg.Polyline([rg.Point3d(u+i*(b+s), v+j*(b+s), 0) for u,v in ring])
     for i in range(3) for j in range(3)]

Drag the slider up from 0 and each crossing grows from a 400 m² square into an octagon of (s + 2c)² − 2c² m². Take c from the cadastral plan, not a guess.

The rule set on your desk

Switzerland has its own rule-set city: La Chaux-de-Fonds, laid out from 1835 by Charles-Henri Junod with streets facing the sun. Kay’s Extruding Earth, a PAZ Building System Specialist Title project, came at the same logic from the other side, generating plots, roads and building types from one editable pattern in Archicad and Grasshopper. Before your office proposes anything for an existing European grid, write down its block, street and corner rules, then test which single change gives the most street back to people.