Spatial masking
Do not weaken the authoritative record merely because the public does not need the exact location. A better pattern is to retain the best authorised geometry in a restricted source and create a separate, documented publication derivative at the level of precision needed for the audience.
What spatial masking can do
Methods include:
- reducing coordinate precision
- aggregating points into areas
- publishing a locality rather than a point
- simplifying polygons
- displaying only above or below particular map scales
- suppressing sensitive attributes
- using a buffer or broad alert area
- publishing counts rather than locations
- omitting geometry entirely
- controlled displacement or jitter where justified
No method is universally safe.
Generalise at publication, not collection
GBIF's current georeferencing guidance recommends recording and storing georeferences at the best available resolution and precision, then generalising when sensitive information is shared or published. It explicitly discourages randomisation as a universal approach and recommends documenting the degree of generalisation.
For Māori GIS, the same architecture is useful:
This preserves future analytical and evidential value without publishing unnecessary precision.
Jitter can create new problems
Randomly shifting a point can make the true location less obvious, but it can also put the feature on the wrong property, marae, waterway or household. A user may then make a false inference from the displaced point.
For many cultural datasets, a deliberately generalised area or named locality is easier to explain than a plausible-looking false point.
Document what you changed
A public derivative should state that it has been generalised and, where safe, how.
Useful metadata can include:
- source precision retained internally
- publication precision
- method of generalisation
- intended use
- warning against site-level interpretation
- date produced
- authority or approval process
Do not disclose a masking method in enough detail to reverse it where the method itself is security-sensitive.
Masking does not defeat inference
A point moved two kilometres may still be identifiable from:
- land ownership
- terrain
- vegetation
- access tracks
- historic maps
- archaeological records
- other species observations
- nearby named features
Treat masking as one control within governance, not a mathematical guarantee.
Choose a representation that matches the purpose
| Purpose | Possible representation |
|---|---|
| Public awareness | broad locality or generalised polygon |
| Regional planning | coarse grid, catchment or alert area |
| Authorised consent assessment | restricted buffer or precise view |
| Site protection | exact restricted geometry |
| Public statistics | aggregated counts |
| Highly sensitive knowledge | no spatial disclosure |
Preserve uncertainty too
Masking and uncertainty are different. A source may already have an uncertain location. Do not publish a precise-looking generalised point that hides both the real location and the uncertainty.
GBIF's guidance is useful here: coordinate precision is not the same as coordinate uncertainty. The same distinction should be carried into Māori historical and cultural GIS.
Related pages
Sources
- GBIF — Georeferencing Best Practices
- Swanlund, Schuurman & Brussoni, MaskMy.XYZ: An easy-to-use tool for protecting location privacy, Transactions in GIS.
- Seidl, Jankowski & Clarke, research on geomasking and identification risk, Geographical Analysis.
Last reviewed: 16 August 2026