Read watershed diagrams in ManYue: choose an outlet before tracing divides and upstream areas

A river on the left does not make the page’s entire left half its watershed. Drainage area depends on a chosen outlet and paths. Read an original six-patch diagram in ManYue, tracing destinations before comparing divides and nested subcatchments. Audit contributing areas for a chosen outlet and containment of subcatchments. It supplies no real surveying, automatic GIS delineation or flood prediction.

Name outlets and six land patches

Draw six equal surface patches A through F, each one square unit, with outlets O/P downstream. Define arrows as simplified surface-drainage directions, not wind, roads or groundwater lines. Record boundaries and symbols; an outlet circle is not an extra land patch, and letter order supplies no elevation. For a non-scale drawing, use declared areas rather than screen colour coverage.

Trace every patch to its final outlet

Specify A→B, C→B, B→O and D→E, F→E, E→P. Follow complete chains: O receives A/B/C, P receives D/E/F. C might appear closer to P on the page yet drains to O, so nearest river or left/right placement is insufficient. This model assigns each patch one final outlet. Splitting or artificial transfer requires new conditions rather than universalising this simple card.

Read the divide as a boundary between drainage areas

Add a dashed supplied surface divide between A/B/C and D/E/F, identified as separating high ground. It is not the channel and need not bisect the page vertically. Check opposite-side patches reach different outlets and relate the line to full areas. A river network alone without terrain or declared flow cannot establish an exact real divide. This supplied teaching boundary does not turn pixel tracing into geographic measurement precision.

Add disjoint same-level areas

Each outlet has three one-unit patches, so O and P each have three square units, disjoint here, totalling six. Count B once as a patch rather than again as a channel node. Area is not water volume: three square units do not imply three cubic metres of runoff without precipitation, losses and time. Arrow lengths encode no area here; any width encoding needs its own legend rather than assuming the thicker E→P implies a larger basin.

Avoid adding a nested catchment to its parent

Place an upstream observation outlet at A’s lower boundary, giving its subcatchment area one. Downstream O still includes A/B/C, area three. Adding one plus three double-counts A. Show containment rather than add adjacent numbers automatically. Choosing another observation outlet changes the analysed drainage area without necessarily changing actual flow, unlike physically altering a channel or transfer. An analytical choice is not an edited environment.

Retain distinct surface and subsurface scope

This diagram supplies surface paths only. Geology, permeability and groundwater levels mean its dashed divide does not guarantee an identical subsurface boundary. USGS includes groundwater in watershed discussion; our tracing simplification does not redefine watersheds to exclude it. Added groundwater lines need separate evidence and legend. Without them mark subsurface scope unchecked. Surface drainage toward O also does not establish receipt of every rainfall drop: evaporation, infiltration and storage require a budget.

Check false junctions and cropped boundaries in ManYue

Read the clear PDF whole to locate outlets, then enlarge A→B and C→B and verify explicit confluence. Crossed lines without junctions are not automatically connected. Restore full boundaries after cropping instead of closing a divide from an isolated dashed segment. Colours do not replace the path ledger; letters/arrows should survive grayscale. Share original diagrams without private locations. No real terrain/rainfall data means no flood prediction or land-safety assessment.

Reopen and verify outlets and containment

Reopen and trace each patch to O/P, calculate three, three and total six square units, then explain why A’s one cannot be added again to O’s three. Retain surface scope, divide legend, all chains and unknown groundwater conditions, not merely coloured regions. Re-trace changed outlets, splits or terrain rather than reuse answers. Bookmarks locate material. Another reader should reconstruct scope and counts without inferring automatic GIS analysis or verified real catchment boundaries.

Related guides and sources

Read meander diagrams in ManYue: follow flow before distinguishing outer and inner banks; ManYue maps inside comics: read the legend before checking a route.

Checked on November 15, 2026: Apple public information lists ManYue 2.0.5, requiring iOS / iPadOS 15.0 or later. See the official App Store for published capabilities; verify controls in the installed version.

Method reference: USGS: watersheds, outlets and drainage divides. Materials and numbers are original exercises. Record external reports, paper reasoning and actual reading observations separately, without inventing missing conditions. Sources do not establish new automatic analysis by the app. No step-by-step physical-device, private-server or all-output-environment testing is claimed.