Maps · World: choropleths and the world's countries

ChoroplethLayer washes each area by its value, keyed by its id or a
property's text or number, on one hue's scale from its faintest at the
least value to its strongest at the most; an area without a value reads
as no data. ChoroplethMap lays it on the owner's map, with or without
tiles, and puts a legend of the scale and of no data in the corner; a
value that matches no area is logged once. WorldMap washes Natural
Earth's 110m countries, bundled trimmed by scripts/countries.py, by ISO
3166 alpha-2 code, and fails on a key that is no code. A shape now
paints as one fill and one edge path per world in view.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/theme/maps.rs

@@ -25,6 +25,8 @@ pub struct MapSizes {
     pub cluster: Rems,
     /// The square of the world that gathers pins into one cluster.
     pub gather: Rems,
+    /// A choropleth legend's scale bar.
+    pub legend: Rems,
 }
 
 impl Theme {
@@ -40,6 +42,7 @@ impl Theme {
             heat_reach: px_to_rems(28.0),
             cluster: px_to_rems(32.0),
             gather: px_to_rems(56.0),
+            legend: px_to_rems(96.0),
         }
     }
 }