3 posts tagged with "Historical imagery"

GIS has a habit of making uncertainty look tidy. Put an old plan on a screen, add a modern cadastral layer, draw a line and label it, and suddenly the result looks as though somebody has settled the matter. The line is crisp, the coordinates are precise, the parcel beneath it is authoritative and the aerial image may be sharp enough to see fences and buildings. Everything about the screen tells the viewer that the answer has been found.

A great deal of Māori claimant mapping taught me the opposite. Sometimes the most accurate result is to admit that the answer is not known. Historical land blocks do not always line up cleanly with modern parcels. Rivers move. Surveyors make assumptions. Names change. Plans disagree. Natural features disappear. Areas recorded on paper do not always agree with areas calculated from geometry. Some source plans are missing altogether. The software is always willing to draw a line, but that does not mean the evidence is willing to support one.

In one of the Northland mapping methodologies we had a very useful description for this: State of Unknown. It was not grand terminology. It simply meant that the available information did not justify pretending there was one certain answer. Over time I came to think of it as one of the most useful professional disciplines GIS can offer, particularly in Māori GIS, where whenua is not merely a parcel to be measured and knowledge of place does not become more authoritative simply because it has been converted into coordinates.

I am not Māori and I do not claim to speak from within te ao Māori. What I can describe is what repeated work alongside Māori claimants, practitioners, researchers and communities taught me about the limits of a purely technical way of looking at land and information. GIS tends to begin with objects: points, lines, polygons, parcels and layers. Much of the Māori mapping work I encountered began somewhere more relational, with people, whenua, whakapapa, history, responsibility and the authority to say what a place means. The map could help represent parts of those relationships, but it could never become the relationship itself.

Downloading a historical aerial photograph is only the first step. To compare it meaningfully with current information, the scan often needs to be connected back to place. That sounds like a technical problem, but georeferencing is also an act of interpretation. We are taking an image captured at one time, often for a survey purpose, and relating it to a present-day coordinate system and landscape that may have changed substantially since the photograph was taken.

For Māori GIS that distinction matters. The goal is not to make an old photograph submit neatly to the modern map. Awa may have moved, coastlines may have changed, roads may have been built and landforms altered. A photograph can help reconnect records and memories to whenua, but its position, its meaning and the conclusions drawn from it still need to be checked against other evidence and, where relevant, the people who know the place.

This older workflow used Google Earth Pro's Image Overlay tool to align an image visually. It can still be useful for people who already have Google Earth Pro installed, but it should now be treated as a legacy exploratory method, not the recommended way to build a new repeatable workflow.

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.