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Georeferencing historical maps in QGIS

A scanned plan can contain place names, old roads, waterways, land blocks, pā, kāinga or boundaries that are difficult to compare with modern geography until the image has coordinates. Georeferencing places the old image into a modern coordinate system so it can be compared with other layers.

It does not make the old map more accurate than it originally was.

The workflow​

Conceptual flow

1. Keep the original​

Keep an unchanged copy of the scan and record its source before altering anything. Useful details include archive, collection, plan or report reference, date, sheet number and URL or file reference.

The Provenance and source checking page provides a reusable pattern.

2. Choose control points​

Good control points can be recognised both on the historical image and in modern reference data. Depending on the map these might include:

  • road intersections that have persisted
  • trig points
  • bridges
  • distinctive river junctions
  • survey marks
  • prominent headlands
  • parcel corners where there is strong evidence they are the same feature

Spread points across the map. Six good points around the image are often more useful than twenty clustered in one township.

Avoid using a changing river bend or coastline as if it were fixed unless the purpose is specifically to investigate that change.

3. Open QGIS Georeferencer​

In current QGIS releases the Georeferencer is available from the raster tools. Load the historical image, set the target coordinate reference system and add control points by matching the old image to modern reference layers.

For most Aotearoa project work, NZTM2000 / EPSG:2193 is a useful projected CRS for analysis. If the rest of the project is deliberately using another CRS, keep the workflow consistent.

4. Choose a transformation​

Transformation choice depends on the source image.

  • a clean modern scan of a plan may need only a simple transformation
  • a photographed paper map may contain perspective distortion
  • an old hand-drawn or compiled map may never align perfectly everywhere

Do not chase a tiny error figure by bending a historically imperfect map until it appears precise. The distortion itself can be part of the source.

5. Read residuals as clues​

QGIS reports residual error for control points. Large residuals can indicate:

  • a poor control point
  • the wrong modern feature
  • distortion in the scan or photograph
  • a genuinely different historical geometry
  • an unsuitable transformation

Inspect the map visually as well as reading the number.

6. Save the raster and the control points​

Use filenames that retain the source identity, for example:

MLC_plan_1908_sheet3_original.tif
MLC_plan_1908_sheet3_georef_nztm.tif
MLC_plan_1908_sheet3_georef.points

Do not overwrite the original image.

7. Digitise selectively​

Once the image is georeferenced, create new vector layers for the features actually needed by the research question. Useful fields include:

  • feature wording on source
  • feature type
  • source reference
  • source date
  • sheet/page
  • interpretation note
  • confidence
  • digitised date

A digitised line is an interpretation of what appears on the source. Keep that relationship visible.

Combine with Local AI​

Local AI can help find references to the same place in reports while georeferencing provides the spatial comparison. A useful sequence is:

  1. find candidate names in documents
  2. preserve the source page and wording
  3. georeference an associated map or plan
  4. compare with Gazetteer, parcels, terrain and other evidence
  5. create a checked research layer

See Find ingoa wāhi, Check the places and Archives to map.

Historical imagery is different​

Retrolens aerial photography is already spatially organised and follows a different workflow from georeferencing an arbitrary scanned map. Use Retrolens historical imagery when aerial photography is the source.

Last reviewed: 26 August 2026

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