How to define/delimit/outline a drainage basin. (step 5)
The fifth step is to locate hilltops and ridges between drainage basins. Find the closed contour circles (and almost closed circles) that separate the your drainage network from all of the other drainage networks, and place a dot on each one. (See the red dots below.) Notice that all of the dots below have the blue tributaries on one side and the green tributaries on the other. Hills surrounded by blue tributaries are not marked!
Now find hilltops and ridges around the rest of the basin.
Next step: Drawing the drainage divide.