This tool calculates an index of convergence (or divergence) with respect to overland flow direction. Its meaning is similar to that of plan or horizontal curvature, but produces much smoother results. The calculation uses the aspects of surrounding cells, i.e. it looks to which degree surrounding cells point to the center cell. Index values are percentages, with negative values corresponding to convergent, positive to divergent flow conditions. Plus 100 would be the peak of a summit, 0 an even slope, and minus 100 a pit.