This file illustrates a bug that causes the ground relative z level indicator in the top right corner to use the pre-erosion ground level instead of the current ground level. The south side of the moat has cut through an area where some of the soil has eroded - the area only has one full layer of soil instead of the usual two for the biome - and when the cursor is in this area the displayed ground relative z level is one lower than expected e.g. it displays -1 on the surface instead of 0.