SANJIESAN LORE / Physical geography
Trace a fictional river to one chosen outlet
A river drawn to fill empty space can become difficult to use when a story needs an upstream village and a downstream port. USGS describes a watershed by the common outlet receiving its drainage. For an invented landscape, start with that relationship before decorating the riverbank.
Choose an outlet and a height direction
Draw a small bay, a lake outlet or a point on a larger river. Mark three surrounding ridges with loose pencil strokes, then add arrows from higher ground toward the chosen outlet. These arrows describe your intended terrain; they are not a hydrological simulation. If a river crosses a ridge, decide whether the ridge sketch is wrong, there is a passage through it, or the setting deliberately uses an extraordinary cause. Resolve that choice before adding towns.
Follow a scene along the same water
Invent a delivery that leaves a hillside workshop, passes a junction and reaches the port. On a separate sketch, mark where the delivery enters the river system and which branches it never visits. A settlement on another tributary is not automatically encountered on the journey. Give the junction an obvious landmark if the text will refer to it. This turns the drainage sketch into usable scene geography without inventing exact sailing speeds or travel times.
Check the map from the outlet backward
Starting at the port, trace each tributary backward to its headwater area. Look for disconnected segments, arrows that reverse without explanation, and labels that attach one river name to two unrelated channels. Keep uncertain terrain lightly marked rather than making every line look settled. The useful deliverable is a readable drainage sketch with one worked journey, not a claim that a fantasy continent has been scientifically verified.