Georeferencing Process

Georeferencing in QGIS

Georeferencing in QGIS involves the process of aligning a non-georeferenced image (e.g. a scanned map or aerial photograph) with a georeferenced dataset (e.g. a shapefile or raster layer with known geographic coordinates). Here are the basic steps to georeference an image in QGIS:

1. Load the image to be georeferenced into QGIS by clicking on the "Add Raster Layer" button and selecting the image file.

2. Load the reference layer (the layer with known geographic coordinates) into QGIS.

3. Enable the Georeferencer plugin by going to Plugins -> Manage and Install Plugins -> Installed and checking the box next to "Georeferencer GDAL".

4. Open the Georeferencer plugin by going to Raster -> Georeferencer -> Georeferencer.

5. Click on the "Open Raster" button in the Georeferencer window and select the image to be georeferenced.

6. Click on the "Add Point" button and select a point on the non-georeferenced image that corresponds to a known location on the reference layer. Enter the coordinates of the corresponding point on the reference layer and click "OK".

7. Repeat step 6 for at least three more points, making sure to choose points that are spread out across the image.

8. Click on the "Transform" button in the Georeferencer window to create a transformation between the non-georeferenced image and the reference layer.

9. Save the georeferenced image by going to File -> Save As and selecting a new file name and format for the georeferenced image.

10. Load the georeferenced image into QGIS as a new raster layer and check that it lines up correctly with the reference layer.

These are the basic steps for georeferencing an image in QGIS. However, it's important to note that the accuracy of the georeferencing depends on the quality of the reference data and the accuracy of the points chosen for the georeferencing process.