Using Retrolens to explore historical aerial imagery in Aotearoa
One of the most useful tools for understanding physical change in whenua over time is historical aerial photography. In Aotearoa, the easiest public way to explore much of this imagery is through Retrolens. The photographs can show rivers before they were straightened, wetlands before drainage, roads before widening, forests before clearance or planting, coastlines before reclamation and settlements before later development.
For Māori GIS, however, the value of historical imagery is not that an aerial photograph somehow reveals the complete truth of a place. It is one view, captured from above at a particular moment for a particular survey purpose. It can sit alongside kōrero tuku iho, whānau memory, historical records, maps and knowledge held by people connected to the whenua. Sometimes a photograph confirms something remembered locally. Sometimes it raises a new question. Sometimes it shows physical change without explaining why that change happened or what it meant to the people living there.
Retrolens provides access to scanned aerial photos dating from the mid-1930s through to the late 1980s. This period covers enormous change in land use, drainage, forestry, farming, road construction, river modification and urban expansion. Used carefully, these images can help reconnect documentary records and present-day geography with landscapes that have since been altered.
What Retrolens is
Retrolens is a public viewer for historical aerial imagery held by Toitū Te Whenua Land Information New Zealand. It allows you to browse, preview and download scanned aerial photographs captured during government and private survey flights.
The site is here:
The imagery itself comes from the LINZ historical aerial photo collection:
Retrolens does not show everything as one seamless historical map. Instead, it exposes individual photo frames much as they were captured during survey flights. That matters because each image has its own date, scale, orientation, distortion and coverage. The photograph is evidence from a moment in time rather than a timeless basemap.
Why this imagery matters for Māori GIS
For many Māori land blocks and rohe, some of the most significant twentieth-century physical changes happened before the 1990s. Retrolens imagery may show original stream alignments before straightening or diversion, wetlands later drained, pā terraces or other landforms before modification, early forestry boundaries, historic access tracks and roads, or coastline form before reclamation and erosion.
The photograph can be especially powerful when it is viewed with people who know the place. Features that look unremarkable to an outside viewer may have meaning because of whakapapa, occupation, use, memory or events connected with the whenua. The imagery can help locate a discussion, but it does not supply that meaning itself. In that sense, the useful GIS practice is not to treat the photograph as a replacement for kōrero, but as another form of evidence that can be brought into relationship with it.
This distinction is important because historical aerial photographs were generally captured for survey, mapping, planning or land-management purposes rather than to record Māori histories. What the camera happened to capture can still be enormously valuable, but the original purpose of the photograph should not be confused with the purposes for which iwi, hapū or whānau may now choose to use it.
Navigating the Retrolens site
When you open Retrolens, you will see a modern basemap with coloured footprints overlaid. Each footprint represents a single aerial photo. Photos commonly overlap, and different flight runs or years may cover the same area. You can zoom to an area of interest, click a footprint to see photo details, preview the scanned image and download the scan as a JPEG or TIFF.
The metadata panel is important. It includes the flight name or number, year of capture, approximate scale and frame number. Record this information if you intend to use the image later. Keeping the source information with the image is part of keeping the whakapapa of the evidence visible. I do not mean that technical metadata is equivalent to whakapapa in the fuller Māori sense. I mean that information has a lineage: it came from somewhere, was created for a reason and should not become detached from that history simply because it has been downloaded into a GIS folder.
Understanding dates and coverage
Retrolens imagery ranges roughly from 1936 through to the late 1980s, but coverage is uneven. Rural areas used intensively for farming may have good coverage, towns and transport corridors can have multiple surveys, while remote or rugged areas may have fewer flights. Some locations have several useful dates and others only one.
Do not assume that a single photograph tells the whole story. Often the most insight comes from comparing two or three dates and then relating those observations to other information. A wetland may be visible in one decade and gone in another, but the photographs alone will not necessarily explain the decisions, policies, drainage schemes or local experiences behind that change.
Image quality and limitations
These images are scanned photographs. They are not automatically orthorectified and they are not perfectly aligned to modern maps. Film grain, scanning artefacts, distortion near the edges and shadows in steep terrain are all normal. An image can be visually compelling and still be spatially uncertain.
This does not reduce its value. It means the limitations need to travel with the image. If a feature appears to be in one location but the scan has not been properly georeferenced, do not let a crisp GIS point imply more certainty than the photograph supports. If exact positioning matters, use a proper georeferencing workflow and record the control points and limitations.
Downloading imagery for further use
Retrolens allows direct download of scans. Before downloading, decide which frames you actually need, which year best suits the kaupapa and whether one image is sufficient or a small sequence is more useful. Downloading fewer, well-chosen images usually makes later work easier and helps keep the purpose of the research clear.
Keep the untouched original scan and its source details. If you crop, enhance, georeference or annotate the image, save that as a separate derivative rather than replacing the source. This makes it easier for the next person to understand what came from Retrolens and what was added during your project.
Using Retrolens alongside modern basemaps
A practical approach is to view Retrolens alongside LINZ Basemaps:
This helps compare historical features with the current landscape, identify alignment problems caused by terrain, and see features that no longer exist. Modern imagery can orient you, but it should not automatically become the reference against which every older source is forced to fit. Rivers move, coastlines change and cadastral or road systems can alter substantially. Sometimes the difference between old and new is the thing you are trying to understand.
Retrolens is best used first for discovery and interpretation. GIS comes later, once you know what question you are asking.
Retrolens, tikanga and responsibility
Historical imagery can reveal sensitive places even though the underlying photograph is publicly accessible. A scan may show the landscape around an urupā, wāhi tapu, former settlement or another place whose significance is not obvious from the photograph itself. When that image is combined with locally held information, the resulting map can reveal much more than the public source did on its own.
Public access therefore does not remove the need for judgement. Before publishing or redistributing an image, consider the kaupapa, the intended audience, what becomes visible when the imagery is combined with other information, and whether clipping, generalising or withholding detail is more appropriate. Kaitiakitanga in this setting is not a decorative label for data management. It is part of the responsibility that comes with holding and using information whose meaning may extend beyond the technical project.
Where local authority is needed, technical convenience should not make the decision. The fact that an image can be downloaded and georeferenced does not mean every interpretation or derived layer should be published.
Final thoughts
Retrolens is one of the best starting points for historical whenua analysis in Aotearoa because it makes an extraordinary public archive accessible with very little technical effort. For Māori GIS it can provide visual context that modern imagery cannot, particularly when the landscape has been heavily modified.
Its strongest use is not as a machine for replacing memory with photographic evidence. It is as another witness to change. The image can help people see, compare, question and reconnect information to place. The meaning of that place still sits within relationships, history and the people connected to the whenua.
Treat the photograph as evidence rather than truth, keep its source and limitations attached, and let the kaupapa determine what happens next.