 Mapping in QGIS, calculating population density using the Field Calculator. You can perform a field calculation within an existing attribute table to calculate text and numeric fields. In this example, we will create a new field in an existing attribute table to calculate population density. To calculate population density, we will have to divide the population by square area. Right-click on the layer and select Open Attribute Table. Select the Open Field Calculator icon in the top menu bar. Here we will create an expression to output a new field. Name the output field PopDen. Set the output field type to Decimal Number Reel by clicking the drop-down arrow. In this case, we can leave the output field length and precision as the default. Our next step is to create the expression which divides each neighborhood's respective population with its area. In the search bar, search for the field Pop. The results will dynamically appear. Since we are conducting a calculation, we want to select the field Pop2001. Double-click on the field. The Population field will be added to the expression box. Click on the division operator icon beneath the expression box. Automatically, you will get an error stating the expression is invalid. This will disappear once we add our second field to the equation. In the search bar, search for area and double-click on the field which represents your area. In this case, we will double-click on area square kilometers. Select OK. Your new field will be added to the far right of the attribute table. Population density has now been calculated and can be displayed as a choropleth map. For more information on QGIS, visit the UTM Library QGIS playlist.