more GeoJSON awareness

docs/marks/geo.md

@@ -11,8 +11,8 @@ const walmarts = shallowRef({type: "FeatureCollection", features: []});
 const world = shallowRef(null);
 const statemesh = computed(() => us.value ? topojson.mesh(us.value, us.value.objects.states, (a, b) => a !== b) : {type: null});
 const nation = computed(() => us.value ? topojson.feature(us.value, us.value.objects.nation) : {type: null});
-const states = computed(() => us.value ? topojson.feature(us.value, us.value.objects.states).features : []);
-const counties = computed(() => us.value ? topojson.feature(us.value, us.value.objects.counties).features : []);
+const states = computed(() => us.value ? topojson.feature(us.value, us.value.objects.states) : {type: null});
+const counties = computed(() => us.value ? topojson.feature(us.value, us.value.objects.counties) : {type: null});
 const land = computed(() => world.value ? topojson.feature(world.value, world.value.objects.land) : {type: null});
 
 onMounted(() => {
@@ -48,7 +48,7 @@ Plot.plot({
   },
   marks: [
     Plot.geo(counties, {
-      fill: (d) => d.properties.unemployment,
+      fill: "unemployment",
       title: (d) => `${d.properties.name} ${d.properties.unemployment}%`,
       tip: true
     })
@@ -57,7 +57,7 @@ Plot.plot({
 ```
 :::
 
-A geo mark’s data is typically [GeoJSON](https://geojson.org/). You can pass a single GeoJSON object, a feature or geometry collection, or an array or iterable of GeoJSON objects.
+A geo mark’s data is typically [GeoJSON](https://geojson.org/). You can pass a single GeoJSON object, a feature or geometry collection, or an array or iterable of GeoJSON objects; Plot automatically normalizes these into an array of features or geometries. When a mark’s data is GeoJSON, Plot will look for the specified field name (such as _unemployment_ above, for **fill**) in the GeoJSON object’s `properties` if the object does not have this property directly. <VersionBadge pr="2092" />
 
 The size of Point and MultiPoint geometries is controlled by the **r** option. For example, below we show earthquakes in the last seven days with a magnitude of 2.5 or higher as reported by the [USGS](https://earthquake.usgs.gov/earthquakes/feed/v1.0/geojson.php). As with the [dot mark](./dot.md), the effective radius is controlled by the *r* scale, which is by default a *sqrt* scale such that the area of a point is proportional to its value. And likewise point geometries are by default sorted by descending radius to reduce occlusion, drawing the smallest circles on top. Set the **sort** option to null to use input order instead.
 
@@ -70,12 +70,12 @@ Plot.plot({
     Plot.geo(land, {fill: "currentColor", fillOpacity: 0.2}),
     Plot.sphere(),
     Plot.geo(earthquakes, {
-      r: (d) => d.properties.mag,
+      r: "mag",
       fill: "red",
       fillOpacity: 0.2,
       stroke: "red",
-      title: (d) => d.properties.title,
-      href: (d) => d.properties.url,
+      title: "title",
+      href: "url",
       target: "_blank"
     })
   ]
@@ -137,7 +137,7 @@ By default, the geo mark doesn’t have **x** and **y** channels; when you use t
 Plot.plot({
   projection: "albers-usa",
   marks: [
-    Plot.geo(states, {strokeOpacity: 0.1, tip: true, title: (d) => d.properties.name}),
+    Plot.geo(states, {strokeOpacity: 0.1, tip: true, title: "name"}),
     Plot.geo(nation),
     Plot.dot(states, Plot.centroid({fill: "red", stroke: "var(--vp-c-bg-alt)"}))
   ]
@@ -157,7 +157,7 @@ Plot.plot({
   marks: [
     Plot.geo(statemesh, {strokeOpacity: 0.2}),
     Plot.geo(nation),
-    Plot.geo(walmarts, {fy: (d) => d.properties.date, r: 1.5, fill: "blue", tip: true, title: (d) => d.properties.date}),
+    Plot.geo(walmarts, {fy: "date", r: 1.5, fill: "blue", tip: true, title: "date"}),
     Plot.axisFy({frameAnchor: "top", dy: 30, tickFormat: (d) => `${d.getUTCFullYear()}’s`})
   ]
 })
@@ -181,7 +181,7 @@ The **x** and **y** position channels may also be specified in conjunction with
 ## geo(*data*, *options*) {#geo}
 
 ```js
-Plot.geo(counties, {fill: (d) => d.properties.rate})
+Plot.geo(counties, {fill: "rate"})
 ```
 
 Returns a new geo mark with the given *data* and *options*. If *data* is a GeoJSON feature collection, then the mark’s data is *data*.features; if *data* is a GeoJSON geometry collection, then the mark’s data is *data*.geometries; if *data* is some other GeoJSON object, then the mark’s data is the single-element array [*data*]. If the **geometry** option is not specified, *data* is assumed to be a GeoJSON object or an iterable of GeoJSON objects.

src/marks/geo.js

@@ -70,24 +70,6 @@ function scaleProjection({x: X, y: Y}) {
 }
 
 export function geo(data, options = {}) {
-  switch (data?.type) {
-    case "FeatureCollection":
-      data = data.features;
-      break;
-    case "GeometryCollection":
-      data = data.geometries;
-      break;
-    case "Feature":
-    case "LineString":
-    case "MultiLineString":
-    case "MultiPoint":
-    case "MultiPolygon":
-    case "Point":
-    case "Polygon":
-    case "Sphere":
-      data = [data];
-      break;
-  }
   if (options.tip && options.x === undefined && options.y === undefined) options = centroid(options);
   else if (options.geometry === undefined) options = {...options, geometry: identity};
   return new Geo(data, options);

src/options.js

@@ -47,7 +47,7 @@ function floater(f) {
 }
 
 export const singleton = [null]; // for data-less decoration marks, e.g. frame
-export const field = (name) => (d) => d[name];
+export const field = (name) => (d) => { const v = d[name]; return v === undefined && d.type === "Feature" ? d.properties?.[name] : v; }; // prettier-ignore
 export const indexOf = {transform: range};
 export const identity = {transform: (d) => d};
 export const zero = () => 0;
@@ -131,8 +131,24 @@ export function keyword(input, name, allowed) {
 }
 
 // Promotes the specified data to an array as needed.
-export function arrayify(data) {
-  return data == null || data instanceof Array || data instanceof TypedArray ? data : Array.from(data);
+export function arrayify(values) {
+  if (values == null || values instanceof Array || values instanceof TypedArray) return values;
+  switch (values.type) {
+    case "FeatureCollection":
+      return values.features;
+    case "GeometryCollection":
+      return values.geometries;
+    case "Feature":
+    case "LineString":
+    case "MultiLineString":
+    case "MultiPoint":
+    case "MultiPolygon":
+    case "Point":
+    case "Polygon":
+    case "Sphere":
+      return [values];
+  }
+  return Array.from(values);
 }
 
 // An optimization of type.from(values, f): if the given values are already an

test/plots/country-centroids.ts

@@ -5,7 +5,7 @@ import {feature} from "topojson-client";
 export async function countryCentroids() {
   const world = await d3.json<any>("data/countries-110m.json");
   const land = feature(world, world.objects.land);
-  const countries = feature(world, world.objects.countries).features;
+  const countries = feature(world, world.objects.countries);
   return Plot.plot({
     projection: "mercator",
     marks: [

test/plots/us-county-choropleth.ts

@@ -23,7 +23,7 @@ export async function usCountyChoropleth() {
       label: "Unemployment (%)"
     },
     marks: [
-      Plot.geo(counties, {fill: (d) => unemployment.get(d.id), title: (d) => d.properties.name}),
+      Plot.geo(counties, {fill: (d) => unemployment.get(d.id), title: "name"}),
       Plot.geo(statemesh, {stroke: "white"})
     ]
   });