Pick a biome — the column is drawn in depth below the surface, the engine's own coordinate. The stack shows how often each block is the rock at each depth; every layer's end is a fuzzy band, densest where its per-column draw usually lands. Drag a band's core to move where a layer ends, its edges to change the spread. The bars beside the stack are each vein's and fill's depth setting (hatched where its own layer is not the rock, so it cannot act): drag one to move it, its ends to resize; drag a ribbon's inner edge to change abundance. Select a vein and one deposit is drawn beside its bar at the same scale, in the dashed box it is allowed to grow in — that is the size you actually dig into, which the bar alone cannot tell you. The right edge reads depth back as world Y under this biome's mean surface.