How did european countries decide where to draw the new boundaries in africa?

When different European countries in the 17-19 centuries captured the colony-then at some point there was a need to delineate the overseas possessions. Otherwise, we would have to fight much more often and more. And for differentiation, in general, there was only two ways-on natural-geographical basis: on a big river, a mountain ridge. There are such borders in Africa. And if there is no natural geographical characteristic? Then we had to draw on the map.

fairly positive it is 4