Selections

Selections are different than using the Identify tool to highlight a feature and expose its attributes. Selections select a set of features in the Attribute Table. Once attributes are thus selected, you can edit them, export them, or perform more analysis.

There are many ways to make selections in QGIS. Broadly, you can select features manually, by expression, and spatially by location/within distance. Generally manual selections involve clicking individual features on your Map Canvas, whereas selections by expression involve using the Expression Builder within the Attribute Table. The tools to run a selection based on location/distance can be found in the Processing Toolbox. However, these last tools and all the other selection tools can be found in your Selection Toolbar at the top of your project window.

Make sure to add the Selection Toolbar to your project if not already visible.

Manual Selections

Manually the neighbourhood of Downtown Vancouver and export it.

Turn off (hide) all irrelevant layers.

Click the neighborhoods layer in your Layers Panel to ensure it is highlighted.

Select downtown.

Note that you can also select multiple neighbourhoods by holding down the shift key on your computer while you select.

Once you’ve made your selection, export it as a new file. Save your selected features to your project folder. You can do this by right-clicking your neighbourhoods layer in your Layers Panel and choosing Export -> Save Selected Features As…. Save as a shapefile to your workshop folder. Name it downtown and change the CRS to match that of the project.

In your Layers Panel, right-click your parks layer and choose Export -> Save Selected Features As….

Click back to your neighbourhoods layer and make sure to unselect all features.

Select by Expression

If you didn’t know just by looking which neighbourhood of Vancouver was downtown, you could write an expression to select it for you from the neighbourhoods layer.

You can open the expression builder either by clicking the drop-down menu of the second selection tool, or from the layer Attribute Table.

We want to write an expression that selects for the feature whose Name is equal to Downtown.

Rather than writing an expression by hand, we will select the appropriate fields, values, and operators from the drop-downs provided. This ensures no syntax errors are made and our selection runs smoothly.

From the middle panel, expand Fields and Values. Double click on Name to add it to the Expression builder.

Then click the = operator. You will get a warning saying your expression is invalid. That’s okay! We aren’t finished building it.

Finally, we need to indicate what the Name is equal to. In the right-hand panel, click the button for All Unique to display all the unique values for Name in the dataset. Double-click on “Downtown” to add it to the expression. Your expression should now be "Name" = 'Downtown'.

Now click Select Features and then close the expression builder. Hide the layer for downtown you just created previously and you should be able to see your selection worked just the same!

Remember to clear your selection, either in the Attribute Table or main QGIS interface.

Spatial Selections

Select by location allows you to select features in 1 layer based on their spatial relationship with those in another layer using various spatial operators.

Slightly different than the above tool, Select within distance “creates a selection in a vector layer. Features are selected wherever they are within the specified maximum distance from the features in an additional reference layer” (QGIS).

To Do

Use Select by Location to select all cultural-spaces located in downtown, using the are within geometric predicate. Use the layer for downtown you just created!

Use Select within Distance to select all cultural-spaces that are within 200 metres of a vancouver park.

Remember to clear your selection.