This is the whole of music theory drawn as a territory. Drag to pan, pinch or scroll to zoom, or use the +/− buttons.
Gold nodes are learned. A pulsing ringed node is open now, that's your frontier. Grey dashed nodes are still locked.
Tap any node, even a fogged one. A locked node always tells you exactly what to learn first, and jumps you there.
Clearing a region's fog reveals the next one, and its trail draws itself in.
This clears every node you've learned in The Territory and re-fogs the map. This can't be undone.