Seven Grids
San Francisco is not one city laid out once. It is seven surveys that met at awkward angles and never reconciled — plus a third of the street network where the ground refused all of them. Every line here is a federal centreline, coloured by which survey drew it.
Bearing rose
Every metre of centreline, sorted by the direction it runs. The peaks are the surveys. Hover a grid below to light its petal.
What you are looking at
Street bearings across San Francisco are not smoothly distributed. Folded to a quarter-turn and weighted by length, they pile into seven sharp peaks. Each peak is a separate act of surveying, and each one is geographically compact — they name themselves once you plot them.
Three of the seven can be dated from this project's sources. The other four are measured here and not dated, because I have no source for when they were laid out and would rather show a gap than invent a year.
O'Farrell's survey
Market Street driven 120 feet wide on the diagonal, with 100-vara blocks south of it. Measured elsewhere in this project at 274.93 ft per lot — 2.84 ft residual.
Van Ness Ordinance
The ordinance and its 1856 map settle title and extend the grid west over the Western Addition, at its own bearing.
Potter & Humphrey
The Outside Lands surveyed. Richmond and Sunset get their names and the largest, most nearly cardinal grid in the city — a third of all its streets.
The measurements
| Grid | Bearing | Length | Share | Survey | Named for |
|---|
Hair on it — what is unfinished
The grids are classified, not measured. I can colour a street by its survey. I cannot yet tell you each survey's block module, the way O'Farrell's was measured to 2.84 ft. The naive method — cluster by bearing, project onto the perpendicular, read the spacing between parallel streets — fails city-wide, because clustering by angle alone merges parallel grids in different neighbourhoods into one comb. Run against South of Market, whose module is independently known to be 358 × 908 ft, it returns a broad multi-modal mess. Fixing it needs spatial clustering — connected components over a bearing-coloured raster — not just an angle test.
The seven peaks are hand-chosen. 3.5° 9.5° 45° 54.5°
18° 86.5° 59°, tolerance ±2.5°, read off the histogram by eye.
A real treatment would fit them. Change the tolerance and the shares move.
Four grids are undated and four of the seven names are mine, taken from the streets inside them rather than from any source. Bayview, Portola, Lakeside and the Excelsior are described here, not cited.
The unassigned third is a category, not an explanation. It holds real curvilinear planning (Sea Cliff, St Francis Wood), park roads, freeway ramps, and every street that bent to a hill. Those are different things wearing one colour.
Where the grid fails
A third of San Francisco's street length fits none of the seven. Turn off Ungridded and the holes appear: Twin Peaks, Mount Davidson, the Presidio, Golden Gate Park's interior, Sea Cliff, Forest Hill. Those are the places where topography beat the transit — or where, later, someone chose the curve on purpose. The negative space is as much a map of the city as the lines are.