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Retrolens and historical imagery workflows

Last reviewed: 23 August 2026

Historical imagery can help iwi, hapū and whānau understand how whenua and taiao have changed over time, support kaitiakitanga decisions and locate places that may no longer be obvious on the ground. Common kaupapa include identifying pre-forestry landforms and tracks, locating former wetlands and stream paths, understanding river movement, checking coastal change and confirming where sites of significance sat before earthworks, subdivision or plantation rotations.

See examples first​

Before building a workflow, these Matawhenua StoryMaps show what historical and current imagery can reveal:

The examples are useful for understanding possibilities. For evidence or operational decisions, work from the original imagery source and retain its capture date, metadata and alignment limitations.

Sources to use in Aotearoa​

Retrolens​

Retrolens is a public viewer for historic aerial photography from the Crown archive, useful for seeing land-use change across decades.

LINZ Basemaps time layers​

LINZ Basemaps includes scanned aerial imagery layers split around 1 January 1990, useful for quick pre and post comparison.

LINZ archive guidance​

For accuracy notes and background on the Crown archive holdings and processing:

Council and regional imagery portals​

Many councils publish aerial imagery layers and historical collections. These are often already georeferenced and consistent at a regional scale.

Examples include Greater Wellington aerial imagery, Wellington City Council Local Maps, Canterbury historic aerial imagery, Marlborough historic aerial photos and Bay of Plenty Regional Council imagery services.

If a council provides an ArcGIS MapServer or ImageServer layer, it can usually be added directly into GIS software without manual georeferencing.

The Accessing Council GIS Maps and data StoryMap provides a worked example for finding council viewers, data and imagery sources.

A practical approach for change over time​

Use two tracks.

  1. Fast visual comparison for discovery and kōrero.
  2. Accurate georeferencing for evidence, measurement and repeatable mapping.

Decade-on-decade timeline​

Retrolens is often the best single source for a consistent decade sweep. Aim to capture one clear image per decade for the same map extent where coverage permits.

Keep extents, scale, orientation and image dates consistent enough for the comparison to be understood.

Workflow 1: quick comparison​

Use this for early exploration and hui preparation.

  1. Open LINZ Basemaps and switch between historical imagery layers.
  2. Keep the same location and zoom and record the visible date or date range.
  3. Open Retrolens for the same location.
  4. Step through available years and select representative dates.
  5. Record short notes describing visible change and why it matters for the kaupapa.

The swipe and before-and-after examples in Applications of Imagery for kaupapa Māori GIS mapping show how these comparisons can later be communicated.

Workflow 2: Google Earth Pro overlay​

Google Earth Pro allows historical images to be placed as overlays. This supports visual alignment rather than high-accuracy mapping.

Prepare the image, navigate to the area, add an image overlay, adjust transparency and align against stable features such as ridge lines, rock outcrops, river confluences, bridges, long-standing buildings and coastlines.

Use manually aligned overlays for shared visual kōrero and early checking only. Avoid using them for legal boundaries, precise measurement or engineering decisions.

Workflow 3: accurate georeferencing in GIS​

For analysis, measurement or repeatable outputs, use a GIS georeferencing workflow.

In QGIS, load a trusted modern base layer, open the georeferencer, add well distributed ground control points, prefer stable features, choose the simplest suitable transformation, save the georeferenced raster and record accuracy notes.

LINZ guidance: https://www.linz.govt.nz/sites/default/files/Georeferencing%20and%20orthorectification%20guidelines%202014%20.pdf

Māori use cases​

Historical imagery can support work on places altered by later land use, forestry change, waterways, wetlands, coastlines, access routes and former settlement patterns.

It can help identify possible pā terraces, former kāinga indicators, old tracks or wetland form, but imagery does not establish cultural meaning by itself. Work from kōrero and other evidence, digitise possible features separately from confirmed information and respect sensitivity.

The Te Whakapapa o ngā Awa StoryMap complements this workflow with freshwater, catchment and monitoring data sources.

Check the source before using it​

Historical imagery is easy to misuse when the image looks convincing but its date or alignment is uncertain.

For every image you retain, record:

  • provider or archive
  • survey, run or image reference where available
  • capture date or best-supported year range
  • whether the image is scanned, georeferenced or orthorectified
  • coordinate reference system where applicable
  • processing or cropping you performed
  • known alignment or scale limitations
  • the purpose for which you are using it
  • sensitivity or sharing restrictions on any interpretation derived from it

Aerial imagery is evidence of what a camera captured at a particular time. A traced feature or cultural interpretation is a separate derived record and needs its own provenance.

Use Provenance and source checking for the wider method.

Try it now​

Choose one familiar area that has visibly changed.

  1. Open Retrolens and identify two images at least ten years apart.
  2. Record the exact dates or best-supported year ranges before comparing them.
  3. Save or note the source references.
  4. Open current imagery for the same location.
  5. Write three observations describing visible change without interpreting cultural meaning yet.
  6. If useful, georeference one historical image in QGIS and record the control points and transformation used.
  7. Create a review layer containing one possible former track, channel, wetland edge or other feature.
  8. Add source, image_date, confidence, interpretation and review_status fields.
  9. Check the interpretation against another source or local knowledge before moving it into a confirmed layer.

The result should show the difference between observed image evidence and later interpretation.

Explore in Matawhenua​

Use the Matawhenua 2D and 3D viewer to orient yourself around terrain and current place context before comparing older imagery. Use the viewer as an exploration tool, not as a substitute for the original historical image and its metadata.

Tikanga and data safety​

Historical imagery can expose sensitive knowledge.

Decide early what is public, restricted or not shared. Generalise sensitive locations where needed, record permissions and intended use, and store mātauranga alongside imagery in ways that reflect Māori data sovereignty and local kawa.

A public StoryMap should normally use an approved presentation layer rather than exposing the full internal GIS dataset used to produce the analysis.

Documentation template​

For each image record, keep at least source, capture date or year range, area of interest, intended use, processing steps, accuracy note, sensitivity level and the appropriate kaitiaki or decision owner.

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