--- type: CaseStudy title: 'Public Trails: Lawful Access, Computed from Official Records' description: How National Digital built publictrails.au - a provenance-graded spatial pipeline that computes whether you can lawfully visit a wild place, and by which route. resource: https://nationaldigital.com.au/case-studies/public-trails/ tags: - spatial data analysis - geospatial application development - open government data integration - interactive mapping development - Spatial data timestamp: '2026-08-19T00:00:00.000Z' --- # Public Trails: Lawful Access, Computed from Official Records How National Digital built publictrails.au - a provenance-graded spatial pipeline that computes whether you can lawfully visit a wild place, and by which route. ## Can I lawfully go there? A question answered by computation, not opinion publictrails.au computes whether a wild place can be lawfully visited, and by which route - from cadastre, protected-area estates, road reserves and easements, with every fact provenance-graded. ## Architecture Diagram - **Delivery** — Static pages, PMTiles + MapLibre - **Verdict engine** — Versioned inference rules - **Common schema** — Per-jurisdiction adapters - **Official records** — Cadastre, estates, reserves, easements - **Pipeline & CI gates** — Deterministic, fail-closed ## The pilot by the numbers Figures describe the live Gold Coast Hinterland pilot (launched August 2026), built end to end from real Queensland government data. - **Routes refused, with reasons, rather than guessed: 58** — Candidate routes where lawful tenure could not be confirmed were refused with reasons - published honesty rather than a guess. _(Source: National Digital delivery records, 2026)_ - **Routes published, each traced to an official record: 435** — 435 computed routes across 109 places and 549 published pages, each carrying its verdict tier and the evidence chain behind it. _(Source: National Digital delivery records, 2026)_ - **Agreement with the hand-checked route: 30 cm** — The hand-checked ground-truth route for the pilot's golden fixture agrees with the pipeline's computed route to within 30 centimetres. _(Source: National Digital delivery records, 2026)_ - **Provenance grade carried on every fact: A-D** — Every fact is graded from gazetted register (A) to community record (D); community data contributes naming only and is quarantined from the legal chain. _(Source: publictrails.au methodology, 2026)_ **Methodology:** Based on National Digital's delivery records and the project's published methodology; figures describe the shipped pilot region rather than independently audited metrics. ## Review ## Why a system that refuses to answer is more trustworthy Public Trails computes whether a wild place can be lawfully visited, and by which route, from official spatial records alone. Every fact is provenance-graded, a verdict inherits the weakest grade in its evidence chain, and where tenure cannot be confirmed nothing is published. - **Refusal is the load-bearing feature: 58 pilot routes were withheld with reasons rather than guessed.** A verdict ladder that can return no lawful route is what makes the 435 published routes credible. Without the ability to decline, every answer would carry the same unearned confidence and a reader could not tell the difference. - **A verdict is only as strong as the weakest link in its evidence chain, and that grade is published.** Facts are graded from gazetted register down to community record, and the verdict inherits the lowest grade it depends on. Confidence is therefore computed from provenance rather than asserted by the system after the fact. - **Community data is quarantined to naming, so it can never influence a legal conclusion.** OpenStreetMap contributes toponyms under ODbL terms through one-to-one pairing with official features. It is structurally excluded from access reasoning, which keeps every legal claim traceable to official sources only. - **Per-jurisdiction adapters over a common schema mean covering a new state is configuration, not a rebuild.** Source adapters normalise each jurisdiction's data at the boundary, so corridor solving, provenance grading and the verdict ladder never encode state-specific logic and are written and tested exactly once. - **Golden fixtures against hand-checked ground truth let the inference rules improve safely.** The pilot's golden route agrees with the computed route to within 30 centimetres, and any rule change that moves a known-good route fails CI. Correctness already achieved cannot be silently regressed by a later improvement. ## Questions decision-makers ask about this build ### How can software answer a legal question about land access? It does not give legal advice - it computes what the official records support and grades its own confidence. Cadastre, protected-area estates, Crown road reserves and easements are read together under versioned inference rules, and each route receives one of four verdicts: formal track, public estate, corridor with conditions, or no lawful route. A verdict's confidence is the weakest provenance grade in its evidence chain. ### Why is refusing to answer treated as a feature? Because the alternative sends someone onto private land. Where lawful tenure cannot be confirmed, no route is published at all - 58 candidate routes in the pilot were refused with reasons rather than published on a guess. The 435 routes that are published are only worth trusting because the system is willing to publish nothing; a product that always has an answer cannot signal when it should not. ### How is community data such as OpenStreetMap used without contaminating the legal chain? It is quarantined to naming only. Community records know what places are called; official records know the law. OpenStreetMap data is paired one-to-one with official features for toponyms under its ODbL terms and graded at the bottom of the A-to-D provenance scale, so it can never contribute to an access verdict. An evidence chain for a legal claim contains only gazetted and official sources. ### What makes this extend to another state without a rebuild? A common schema with per-jurisdiction source adapters, so the analysis code never sees a state. Each jurisdiction's cadastre, protected-area estates and road-reserve data is normalised at the adapter boundary, which means corridor solving, provenance grading and the verdict ladder are written once and reused. Covering a new state is an adapter and a source manifest, not a second system. ### How do you know the computed routes are actually right? Golden fixtures pin computed routes against hand-checked ground truth, and the pilot's golden route agrees with the pipeline's computed route to within 30 centimetres. Any change to the inference rules that moves a known-good route fails continuous integration, so the rules can keep improving without silently breaking answers that were already correct and already published. ### How are cultural heritage and safety obligations handled? Aboriginal cultural heritage site locations are never ingested, stored or republished, and a fail-closed restricted-register gate in continuous integration enforces that rather than a policy document. Statutory duty-of-care notices are carried on every page, and on-ground signage and temporary closures override every published page by design. The site supports planning; it is never the authority at the gate. ## More of our work - Surgery Waits: Comparable Hospital Waiting Times - how2vote.au: A Provably Neutral Voting Tool *What's next* ## Complex data, hard guarantees? Public Trails turns scattered official records into computed, evidence-graded answers. If your domain needs the same rigour, see how we approach [data analysis and insight platforms](/ai-automation/data-analysis-and-insights) and [system integration](/platform-engineering/system-integration), part of our wider [custom software development](/digital-product-development) work. ## Want a platform like this for your business? Tell us what you're building. 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