How to define/delimit/outline a drainage basin. (step 4)
The fourth step is to define the adjacent drainage networks (streams and rivers). Simply repeat steps two and three for the adjacent drainage basins. It is a good idea to define these drainage networks with a different color (green has been used below, dark for the primary drainage and light for the interpreted streams). The next step will be to locate the hills and ridges that surround the drainage basin, these hills will be located between the two sets of tributaries.
Now, find adjacent tributaries around the rest of the map.
Next step: Locating hilltops between drainage basins.