Digitisation

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Digitisation is the process of converting geographic data from maps or images into digital form commonly represented as vector data. During this procedure, spatial information from maps or images is traced, forming points, polylines, or polygons. To digitize data for a new dataset you always have to start with creating the dataset before filling it with digitized data.

The Digitisation Toolbar in QGIS

• Digitisation in QGIS is done primarily with the digitisation toolbar. To activate the toolbar, navigate to View -> Toolbars -> Digitisation Toolbar.

Creating a new layer

1. In the top bar, navigate to Layer -> Create Layer -> New GeoPackage Layer or New Shapefile Layer.

2. A new window will open. Here you can specify the layer properties.

3. Under Database, click on the three points and navigate to the folder where you want to save the new dataset.

4. shapefile specific: Set the file encoding to UTF-8.

5. Geometry type: Select the type of geometry you want to digitise: points, lines or polygons.

Tip

If you plan to perform distance-based calculation with the new dataset, make sure to use a metric CRS. The units of measurements for the layer will be in meters and not degrees (see Metric and Geographic Coordinate Reference Systems)

6. Select the CRS (Coordinate Reference System) you want to use for the new layer. By default it is set to the project CRS. If you want to change the CRS click on .

7. Under New Field, you cann add columns to the new layer. Here you can define what kind of information/data will be available in the attribute table for each feature.

   • Name: Give the new column a name representing the information you want to store in it.

   • Type: Here you can select the data type for the new column. For example, Text will add a new column with string (text) data. For numerical data you can choose Whole number or Decimal number.

   • Maximum Length defines the maximum number of characters the field can have. This is relevant for the length of text or the precision of decimal numbers. For example, you might want to set a high maximum length for text field if you want to long street names such as “Martin Luther King Jr. Boulevard” (34 characters).

   • Click on to add the new column to the Fields List.

8. Once you are done adding the fields, click OK.

Adding geometries to a layer

Creating point data

1. Select the point layer you want to add data to in the Layer panel

2. Go to the digitsation toolbar and click on. No the layer is in the editing mode.

3. Click on .

4. Left-click on the feature you want to digitise.

5. Once you click, a window named [Your Layer Name]- Feature Attribute will appear. Here you can add the information about this feature to the different columns, based on the attribute table of the layer.

5. Once you are done with digitisation to save your edits.

6. Click again on to end the editing mode.

Creating line data

The method is similar to digitising a point (see above). First you have to created a new line layer or use an existing one.

Attention

If you create a new line layer remember to change the geometry type into lines because we are creating lines data now.

1. In the layers panel, select the line layer to which you want to add data.

2. In the digitisation toolbar, click on . Now the layer is in editing mode.

3. Click on .

4. Create the line on the map canvas by lef-clicking to add vertices. When you are done, right-click on the last point to finish editing the geometry.

5. A new window titled [Your Layer Name]- Feature Attribute will appear. Here you can fill in the column information for the feature.

6. Once you are done with digitisation, click on to save your edits.

7. Click on the icon again to end the editing mode.

Creating polygon data

1. In the layers panel, select the polygon layer to which you want to add data.

2. Click on to start the editing mode.

3. Click on Capture Polygon to add polygons.

4. Draw a polygon in the map canvas using Lef-click. Right-click will finish the polygon creation and join the first and the last point you have added.

5. A new window will open. Here you can add the column information for this feature.

6. Save edits by clicking on the icon and exiting the edit mode by clicking on the icon.

Modifying existing geometries

1. In the layers panel, select the layer with the geometry you want to edit by clicking on it. It will appear blue.

2. In the digitising toolbar, click on start edit mode.

3. In the digitising toolbar, click on . Now, you can move and edit vertices of geometries.

4. Once you are done, don’t forget to exit the editing mode by clicking on and saving your edits.

Adding Ring to existing polygon layer

In QGIS, adding rings to polygons is done with the “Advanced Digitisation Toolbar”. To activate the toolbar, navigate to View -> Toolbars -> Advanced Digitisation Toolbar.

1. Click on to start the editing mode of a polygon layer.

2. Click on (e.g. map the inner courtyard of a building, or - as shown in the video - create a circle to mark an isle in the lake).

Further resources

The YouTube Video below shows the whole process of digitizing polygons in QGIS in some more detail. Note that the YouTuber is using an older version of QGIS, so things might be different in your version.