Calculate the area of habitat types. To do this, we first need to ‘collect geometries’ so that all the Habitat groups only have one table entry. This means that when we calculate the area for habitat, we will get the total area for each habitat type not just the area for each polygon. Skip to video.
Use Geometry Tools > Collect Geometries:
Select Group as the attribute to group the polygons into, as shown.
Now, when you open the attribute table, you will only have one entry for each habitat type.
You can clean up the table by deleting all attributes except the group name.
- Select the edit table button
- The delete attributes button and select all the attributes except “Group” and delete them.
Now, we will calculate the area of each habitat type. To do this, we must set the coordinate system, so QGIS knows how to calculate the area.
- Select the project > properties window.
- Set the projection to ADG66.
You might need to use the filter search for AGD66 or type in 4202, which is the code number for this projection.
To Calculate the open the field calculator tool:
- Click Create a new field
- Name the output field “area km2”
- Find “$area” function in the field calculation functions list.
- Enter the calculation “$area/1000000”. The default area will be in m2. Dividing it by one million will give km2.