Box selection and linked maps

Shift-drag either map to select what the box encloses, Alt to add to the selection, Escape to abandon it, and a box over nothing clears it. A plain drag still pans, and the click that ends a drag is not a click on whatever it landed on. Both maps declare the same link: { group }, so a selection made on one applies to the other and everything unselected steps back on both. Linked selection is a licensed feature, so this pair carries the evaluation watermark.

Anchors, not bounding boxes

A box tests each candidate's label anchor, which sits inside the shape. Bounding-box intersection reads plausibly and behaves badly: Alaska's bbox spans the Pacific, so any box touching the Aleutians would select it, and a box over the Great Lakes would select half a dozen states it does not visibly cover. Point marks are tested at their own position, and the automatic basemap is left out, since a country drawn only so bubbles have a coastline carries no data and could not filter anything.

interaction: {
  selection: { multiple: true, rectangle: true, modifier: 'shift' },
},
states: { muted: { opacity: 0.25 } },   // 1 turns dimming off
link: { group: 'us-dashboard', filter: 'bidirectional' },   // or 'emit' / 'receive'