Add support for projections to the standalone Plot.scale function by Fil · Pull Request #2427 · observablehq/plot

Fil · 2026-04-13T15:46:32Z

e.g. Plot.scale({projection: {type: "mercator", width, domain: …}}).

When merged, we must add this to the changelog PR #2426:

The standalone [Plot.scale](https://observablehq.com/plot/features/scales#scale) function now also supports projections.

```js
const projection = Plot.scale({projection: {type: "mercator"}});
projection.apply([-1.55, 47.22]) // [316.7, 224.2]

const plot = Plot.plot({projection, marks: [Plot.sphere()]});
```

_e.g._ Plot.scale({projection: {type: "mercator", width, domain: …}}).

docs/features/scales.md

src/scales.d.ts

src/scales.js

mbostock

As far as testing goes, I’m hoping that we can test this new implementation against the existing (more wasteful) one. This:

Plot.plot({projection: {type: "mercator"}}).scale("projection")

Should be the same as this:

Plot.scale({projection: {type: "mercator"}})

src/scales.d.ts

Co-authored-by: Mike Bostock <mbostock@gmail.com>

note that the terse definitions here are for Plot.scale({projection}), and get overridden by more detailed definitions in Plot.plot()

…ction)

Fil · 2026-04-14T12:05:14Z

src/dimensions.d.ts

@@ -1,3 +1,21 @@
+/** Options for specifying the dimensions of a plot or standalone projection. */


note that the terse definitions here are in fact only for Plot.scale({projection}), and get overridden by more detailed definitions in Plot.plot(), i.e.

plot/src/plot.d.ts

Line 11 in 1c6b239

/**

Fil added 2 commits April 13, 2026 17:26

Add support for projections to the standalone Plot.scale function

8957bff

_e.g._ Plot.scale({projection: {type: "mercator", width, domain: …}}).

document Plot.scale(projection)

78ba878

Fil requested a review from mbostock April 13, 2026 15:46