Georeferencing and Digitizing in QGIS – Series 4

Many valuable maps and spatial records still exist as scanned images. Examples are historical plans, paper-based surveys, architectural layouts e.t.c. While informative, these images are not yet usable within a GIS environment until they’re spatially referenced and digitized.

In this fourth part of our QGIS blog series, we’ll introduce two essential processes:

• Georeferencing: aligning a scanned image with real-world coordinates
• Digitizing: converting visible features on that image into structured vector data

What is Georeferencing?

Georeferencing is the process of assigning real-world coordinates to a scanned map or image, making it usable in GIS environments. It aligns the image with known map projections or co-ordinate systems. Imagine having a scanned paper map of a neighbourhood. QGIS allows you to “stretch” that map so it fits perfectly over your real-world basemap.

How to Georeference in QGIS

Step 1: Go to layer ribbon > Georeferencer

Step 2: Load Your Image: Click “Open raster” and choose your scanned map/image

Step 3: Add Ground Control Points (GCPs)

• Use Add Point tool to select a location on the image
• Then choose the corresponding real-world location on your basemap (or input coordinates)

Step 4: Set Transformation Settings

• Click the gear icon 
• Set:
  • Transformation Type: usually Polynomial 1
  • Target SRS: Choose a CRS like EPSG: 3857 (WGS 84) or EPSG: 32632 (UTM)
  • Output raster path

Step 5: Start Georeferencing: Click the Play (Start Georeferencing) button

Step 6: Image has been successfully georeferenced

What is Digitizing?

Digitizing involves manually tracing features (like roads or buildings) from a map or image into a new vector layer.

How to Digitize in QGIS

Let’s say you want to trace boundary lines from your georeferenced map.

Step 1: Create a New Vector Layer

Go to Layer > Create Layer > New Shapefile Layer > Choose geometry type: Point, Line, or Polygon > Add attribute fields (e.g., Name, Type) > Click OK and save the file

Step 2: Start Editing

Right-click your new layer → Toggle Editing

Step 3: Save and Stop Editing: Click Save Edits > Then click Toggle Editing again to stop

In this post, we completed the core journey with vector data by learning how to georeference scanned maps and digitize new spatial features. These steps are essential for transforming analog or static resources into usable GIS layers.

With vector basics behind us, our next post will shift focus to another important GIS data type which is raster data. We’ll explore what it is, where to get it, and how to visualize and interpret it in QGIS.