How to play Choose coastlines for four named islands, then draw the fifth. On a phone, choose or draw your shape, then tap Next to size and place it. Change shape keeps your outline, size and position. On desktop, shape and map share one workspace. Your island previews only after you choose or draw an outline.
Drag the map outside the island to move it behind the reticle. Pinch or scroll to zoom for finer positioning. Drag the island itself to move just the island without panning the map. Drops inside the middle third of both map width and height stay where you put them, including the boundary. Release outside either middle third to smoothly recenter; reduced-motion settings skip that animation. The map distance scale uses miles for an en-US browser locale and kilometers otherwise, measured at the projection’s center.
Resize with the diagonal-arrow handle, the size slider, or Command/Ctrl + scroll over the map (scroll up to enlarge, down to shrink). Trackpad gestures sent as Ctrl + scroll also resize during play; a two-finger touch pinch still zooms the map. All size controls share the same limits and change physical size, not map zoom. Hold Shift while scrolling for finer sizing.
Guess submits your island’s location and reveals the answer. Try again keeps your shape and size.
Completed attempts and their replay geometry are kept in this browser’s IndexedDB storage, including retries. Clearing site data removes this local history. Unsubmitted edits are not saved.
How scoring works Shape is 80% outline overlap and 20% physical size. We center both silhouettes, normalize their longest dimension, and sample their intersection-over-union on a 72 × 72 grid. North-up orientation and proportions still matter. Size uses the equivalent-area width ratio: 100 × exp(−1.8 × |ln(ratio)|).
Location uses great-circle distance between the placed anchor and the real island’s center: 100 × exp(−ln(2) × (distance/tolerance)²). Tolerance is 70% of the real island’s equivalent-area radius, with a 35 km minimum. Making your island bigger never widens the target. Camera zoom affects neither score. The final score is the mean of Shape and Location.
Display-only detail levels simplify the 0.018° map at distant zooms; the original coastlines still frame reveals and 0.003° silhouettes still score. Nearby islets remain; the whole target land polygon is removed. Draw one continuous closed outline; finger-sized endpoint gaps are joined locally. Separate strokes join in drawing order.
Coastlines: Natural Earth 1:10m land, public domain . Explore demos .
Keyboard: on the map, arrows move the map, Shift+arrows fine-tune, +/− zoom. Tab to the island and use arrows to move it; releasing outside the middle third of either map dimension recenters. On the resize handle, arrows change size, Shift+arrows fine-tune, Home/End reach the size limits. Tab to Guess and press Enter to submit.
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