Skip to main content

Retrolens and historical imagery workflows

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.

Sources to use in Aotearoa​

Retrolens (1936 to 2005, variable coverage)​

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 (quick comparison)​

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

LINZ historical aerial imagery archive context and guidance​

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

Council and regional imagery portals​

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

A practical approach for change over time​

Use a two track approach.

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

Decade on decade timeline (1940s to 2000s)​

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

  • 1940s: early aerial coverage, lower clarity but valuable pre development context
  • 1950s: continued rural patterns and early forestry expansion
  • 1960s: significant land development and roading changes
  • 1970s: plantation forestry and intensification become visible
  • 1980s: urban expansion and infrastructure growth
  • 1990s: baseline for many modern planning records
  • 2000s: later Retrolens coverage before modern council and LINZ programmes Keep extents, scale, and orientation consistent across decades.

Workflow 1: quick comparison using LINZ Basemaps and Retrolens​

Use this for early exploration and hui preparation.

  1. Open LINZ Basemaps and switch between pre 1990 and post 1989 scanned aerial imagery.
  2. Keep the same location and zoom, capture screenshots, and label with year range and source.
  3. Open Retrolens for the same location.
  4. Step through available years and select representative dates for each decade.
  5. Record short notes describing visible change and why it matters for the kaupapa. This approach is often sufficient for wānanga and early planning.

Workflow 2: Google Earth Pro overlay for quick alignment​

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

  1. Prepare the image by cropping and improving contrast if needed.
  2. Open Google Earth Pro and navigate to the area.
  3. Add an image overlay.
  4. Align using corners, edges, and transparency.
  5. Match stable features such as ridge lines, rock outcrops, river confluences, bridges, churches, long standing buildings, and coastlines.
  6. Save overlays as KMZ and export any traced features as KML. Use this for shared visual kōrero and early checking only. Avoid using overlays 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.

QGIS​

  1. Load a trusted modern base layer.
  2. Open the georeferencer and load the scanned image.
  3. Add well distributed ground control points.
  4. Prefer stable features and avoid vegetation edges and moving waterways.
  5. Choose the simplest suitable transformation.
  6. Save the georeferenced raster and record accuracy notes.

ArcGIS Pro​

ArcGIS Pro provides a structured georeferencing workflow.

Māori use cases​

Locating sites before land use change​

Historic imagery can help identify features altered or removed by later land use.

  • pā terraces or borrow pits affected by forestry
  • former kāinga indicated by orchards, shelter belts, house pads, or tracks
  • urupā access routes before subdivision or plantation rotations
  • mahinga kai wetlands before drainage or channel straightening Work from kōrero first, then use imagery to support understanding. Digitise broadly, assign confidence levels, and respect sensitivity.

Forestry change detection​

Compare consistent snapshots.

  • pre plantation
  • early establishment
  • mature canopy
  • post harvest and replanting Look for stream changes, skid sites, roading, culverts, and erosion.

Waterways and wetlands​

Historic imagery can reveal braided channels, former wetland extent, oxbows, and abandoned meanders. These insights support restoration planning and catchment kōrero.

Tikanga and data safety​

Historic imagery can expose sensitive knowledge.

  • Decide early what is public, restricted, or not shared.
  • Generalise sensitive locations or use buffers.
  • Record permissions and intended use.
  • Store mātauranga alongside imagery in ways that reflect Māori data sovereignty and local kawa.

Documentation template​

For each image record.

  • Source
  • Capture date or year range
  • Area of interest name
  • Intended use
  • Processing steps
  • Accuracy note
  • Sensitivity level
  • Kaitiaki or decision owner