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Source–Sink Patch Map

Classification map — instantiates Source–Sink Viability Management

Lays out every unit as a labelled patch — source, sink, neutral, or contested — coloured by measured net balance, so the asymmetric structure of who is quietly carrying whom becomes visible at a glance.

The Source–Sink Patch Map is the foundational artifact of the whole archetype: it turns a coupled system into a labelled picture in which every unit is drawn as a patch and tagged with the role it actually plays — source, sink, neutral, role-switching, unknown, or contested — where the tag is driven by measured net balance, not by whether the patch merely looks busy or occupied. Its defining move, the thing that separates it from every sibling, is that it classifies on the sign of net balance after each unit's own renewal is protected — never on presence, size, or activity — so a bustling, fully-occupied unit is still coloured a sink if it consumes more than it makes. The map says who is what, right now, and how confidently; it does not forecast, price, or track over time.

Example

A land trust manages a reserve of eight meadows for a declining butterfly. Every meadow is occupied, which for years read as "the population is healthy." The patch map is where that story breaks. For each meadow the team estimates its net demographic balance — offspring surviving to disperse against adults lost — and colours the patch by whether it runs positive or negative. Three come out green (they export dispersers), two neutral, and three deep red: they stay occupied only because dispersers keep arriving from the green patches — classic demographic sinks. One red patch is tagged contested, because it may be a pseudo-sink that would hold its own at lower density if immigration stopped. Every patch carries a confidence and an "as of spring ≈2026" horizon. The finished map reframes the reserve from "eight occupied meadows" to "three sources quietly carrying three sinks" — and that single reframing is what the budget, the guardrails, and every exit decision downstream will hang on.

How it works

  • Classify on net balance, not occupancy. The rule that keeps the map honest: role = sign of local production minus loss, measured after protecting the unit's own renewal — never presence/absence or activity level. Occupancy is precisely the trap the archetype exists to escape.
  • Six-way vocabulary. Source / sink / neutral / role-switching / unknown / contested — the last two are first-class, so the map can admit what it does not yet know instead of forcing a false binary.
  • Confidence and horizon per patch. Every tag is dated and carries a confidence, because roles drift after shocks, restoration, seasonality, or growth.

It is deliberately a snapshot: no trend lines, no forecasts, no prices — those belong to the dashboards and the model-side siblings.

Tuning parameters

  • Unit granularity — whether a patch is a single site or a whole region; finer patches reveal truer roles but multiply the net-balance measurements you must fund.
  • Net-balance window — a single snapshot versus a multi-season average; short windows mislabel a unit that was merely having a bad shock.
  • Confidence encoding — how visibly unknown and contested are marked; hiding them buys a cleaner-looking map at the cost of false certainty.
  • Role vocabulary — collapsing to a stark source/sink binary versus carrying the full six categories; the binary is legible but erases role-switchers.
  • Redraw trigger — refresh on a fixed calendar versus on shocks and restoration events; event-driven redraws catch reversals a calendar misses.

When it helps, and when it misleads

Its strength is that it kills the aggregate-survival illusion — the reason the archetype exists — by making local nonviability visible even while the whole still looks alive, and it gives every other mechanism a shared, testable classification to build on. It fails when it is trusted as permanent: a map is a snapshot, roles drift, and a stale map hardens into dogma that keeps support flowing to a patch that has since recovered — or starves one that has since collapsed. The classic misuse is drawing it after a decision, colouring the patches to justify a subsidy or a closure someone already wants, rather than measuring first. The subtler error is mistaking a pseudo-sink for a true demographic sink,[1] which condemns a viable unit as a lost cause. The discipline that guards against all three: date every map, carry the confidence tags forward, and let the reclassification ritual re-measure net balance rather than re-touching the colours by hand.

How it implements the components

The Patch Map fills the classification core of the archetype — the components that establish what the units are and which role each plays — and nothing downstream of that:

  • unit_of_persistence — it fixes what actually has to persist (each meadow, site, account, or node) by drawing it as a discrete patch, so the classification isn't rhetorical.
  • source_sink_role_map — the coloured, confidence-tagged six-way classification is the role map.
  • net_balance_measurement — the production-minus-loss measure that decides each patch's colour.

It does NOT monitor each unit's health or dependency over time — that's the Source Depletion Dashboard and Sink Dependency Dashboard — nor forecast future colonisation and extinction, which is the Metapopulation Model's job.

Notes

The Patch Map holds the classification; it does not maintain it. Keeping it distinct from the Role Reclassification Review — the ritual that revisits and updates roles — is what lets the map stay a clean, dated snapshot rather than an ever-edited palimpsest whose history is lost.

References

[1] A pseudo-sink looks like a sink — at its current, immigration-inflated density local deaths exceed local births — but would persist at a lower equilibrium density if the immigration stopped; it is genuinely viable, unlike a true demographic sink, which winks out without continual rescue. Confusing the two is the patch map's most consequential classification error. ↩