Update CHANGELOG

Author: mbostock

CHANGELOG.md

@@ -4,7 +4,7 @@
 
 *Not yet released. These are forthcoming changes in the main branch.*
 
-The new [geo mark](https://observablehq.com/@observablehq/plot-geo) renders GeoJSON geometries.
+The new [geo mark](./README.md#geo) renders GeoJSON geometries such as polygons, lines, and points. Together with Plot’s new [projection system](https://observablehq.com/@observablehq/plot-projections), Plot can now produce thematic maps. For example, the choropleth map below shows unemployment rates by U.S. county.
 
 [<img src="./img/choropleth.png" width="640" alt="A choropleth of unemployment rate by U.S. county">](https://observablehq.com/@observablehq/plot-geo)
 
@@ -21,25 +21,26 @@ Plot.geo(counties, {fill: (d) => d.properties.unemployment}).plot({
 })
 ```
 
-Naturally, it works with Plot’s core features, including scales, legends, and faceting.
+The new top-level [**projection** option](./README.md#projection-options) controls how geometric coordinates are transformed to the screen and supports a variety of common geographic projections, including the composite U.S. Albers projection shown above, the Equal Earth projection, the Mercator projection, the orthographic and stereographic projections, several conic and azimuthal projections, among others. Projections can be fit to geometry using the projection.**domain** option, and rotated to an arbitrary aspect using the projection.**rotate** option.
 
-[<img src="./img/faceted-map.png" width="930" alt="A dot map of Walmart store openings faceted by decade">](https://observablehq.com/@observablehq/plot-geo)
+[<img src="./img/orthographic.png" width="640" alt="A world map using the orthographic projection, centered somewhere around San Antonio, Texas">](https://observablehq.com/@observablehq/plot-projections)
 
 ```js
 Plot.plot({
-  width: 975,
-  projection: "albers",
-  fx: {tickFormat: (d) => `${d}’s`},
-  facet: {data: walmarts, x: (d) => Math.floor(d.date.getUTCFullYear() / 10) * 10},
+  height: 640,
+  inset: 1,
+  projection: {type: "orthographic", rotate: [100, -30]},
   marks: [
-    Plot.geo(statemesh, {strokeOpacity: 0.1}),
-    Plot.dot(walmarts, {x: "longitude", y: "latitude", r: 1, fill: "currentColor"}),
-    Plot.geo(nation)
+    Plot.graticule(),
+    Plot.geo(land, {fill: "currentColor"}),
+    Plot.sphere()
   ]
 })
 ```
 
-The new top-level [**projection** option](https://observablehq.com/@observablehq/plot-projections) controls how geometry coordinates are mapped to the screen. While primarily for the geo mark, it works automatically with most of Plot’s other mark types. For example, here is a map using vectors to show county-level vote margins in the 2020 U.S. presidential election.
+The new graticule convenience mark renders meridians and parallels (lines of constant longitude and latitude), while the sphere convenience mark draws the outline of the sphere.
+
+Plot’s projection system works automatically with most of Plot’s mark types, including dots, vectors, lines, and rects. For example, the map below uses vectors to show county-level vote margins in the 2020 U.S. presidential election: a margin for Biden is shown as a blue left-pointing arrow, while a margin for Trump is shown as a red right-pointing arrow; the length of the arrow is proportional to the margin.
 
 [<img src="./img/vector-map.png" width="640" alt="An arrow map showing the county-level vote margins in the 2020 U.S. presidential election; a margin for Biden is shown as a blue left-pointing arrow, and a margin for Trump is shown as a red right-pointing arrow">](https://observablehq.com/@observablehq/plot-projections)
 
@@ -64,7 +65,7 @@ Plot.plot({
 })
 ```
 
-With the line mark, it’s not just a point projection; the line mark automatically passes line geometry through the projection, allow projections to interpret line segments as geodesics and to clip or cut as needed. For example, the route of the HMS *Beagle* shown below is automatically cut when it crosses the antimeridian.
+For the [line mark](./README.md#line), the specified projection doesn’t simply project control points; the projection has full control over how geometry is transformed from its native coordinate system (often spherical) to the screen. This optionally allows line geometry to be represented as [geodesics](https://en.wikipedia.org/wiki/Geodesic), which are sampled and clipped during projection. For example, the map below shows the route of Charles Darwin’s voyage on the HMS *Beagle*; note that the line is cut when it crosses the antimeridian in the Pacific ocean. (Also note the use of the *stroke* channel to vary color.)
 
 [<img src="./img/beagle.png" width="640" alt="A map of the route of the HMS Beagle, 1831–1836; color indicates direction, with the ship initially departing London and heading southwest before circumnavigating the globe">](https://observablehq.com/@observablehq/plot-projections)
 
@@ -80,7 +81,25 @@ Plot.plot({
 })
 ```
 
-Plot’s projection system works with Plot’s transforms. For example, the map below demonstrates using the hexbin transform to aggregate projected locations into local hexagons.
+Plot’s new geo mark and projection system work with Plot’s other core features, including scales, legends, faceting, and transforms. For example, here is a faceted dot map showing openings of Walmart stores over five decades.
+
+[<img src="./img/faceted-map.png" width="930" alt="A dot map of Walmart store openings faceted by decade">](https://observablehq.com/@observablehq/plot-geo)
+
+```js
+Plot.plot({
+  width: 975,
+  projection: "albers",
+  fx: {tickFormat: (d) => `${d}’s`},
+  facet: {data: walmarts, x: (d) => Math.floor(d.date.getUTCFullYear() / 10) * 10},
+  marks: [
+    Plot.geo(statemesh, {strokeOpacity: 0.1}),
+    Plot.dot(walmarts, {x: "longitude", y: "latitude", r: 1, fill: "currentColor"}),
+    Plot.geo(nation)
+  ]
+})
+```
+
+As another example using the same dataset, the map below uses the hexbin transform to aggregate Walmart store opening into local hexagons.
 
 [<img src="./img/hexbin-map.png" width="640" alt="A bivariate hexbin map of Walmart store openings; within each hexagonal area, size indicates the number of Walmart store openings, and color indicates the year of the first opening">](https://observablehq.com/@observablehq/plot-projections)
 
@@ -100,7 +119,7 @@ Plot.plot({
 })
 ```
 
-While a variety of basic projections are included by default, Plot’s projection system can be extended using any implementation that is compatible with D3’s *projection*.stream interface. This includes the existing d3-geo-projection and d3-geo-polygon libraries. For example, here is a world map using Goode’s interrupted homolosine projection.
+In addition to the included basic projections, Plot’s projection system can be extended using any projection implementation compatible with D3’s [projection stream interface](https://github.com/d3/d3-geo/blob/main/README.md#streams). This includes all the projections provided by the [d3-geo-projection](https://github.com/d3/d3-geo-projection) and [d3-geo-polygon](https://github.com/d3/d3-geo-polygon) libraries! For example, here is a world map using Goode’s interrupted homolosine projection.
 
 [<img src="./img/goode.png" width="640" alt="A world map using Goode’s interrupted homolosine projection">](https://observablehq.com/@observablehq/plot-projections)