How to align maps using the Georeferencer in QGIS

Note: This is useful for lining up maps from different flight days or different sensors so a single plot grid can extract all the data, or so comparisons can be made between them. For example, you could use an NDVI-based plant/soil classification layer to remove soil pixels from a thermal camera. But it is optional and depends on your needs!

See also: https://docs.qgis.org/3.40/en/docs/user_manual/working_with_raster/georeferencer.html

1. Layer → Georeferencer
   
2. In the new window: File → Open Raster.

 

3. Open the tif file of interest (to be corrected).
4. Click a point that can be compared between maps, and in new window that pops up, click “from Map Canvas”. Then select the corresponding point in the other map, and click “OK”

5. Repeat the step above for 10-15 points.
   
6. Click Settings → Transformation settings:

1. For transformation type, click the drop-down and select “Thin plate spline” (I don’t recommend “linear”, which will only move+rotate+expand/contract the raster, not correct spatial distortions!)
2. For resampling method, click “Cubic”
3. Next to output folder, click the three dots to select a folder and file name
4. At the bottom, ensure that the box for “Load into project when done” is checked.
5. Click “OK”

7. Click the green play button (“start georeferencing”).
8. Check the new layer  ensure it aligns with your other files!