Catalogue number: Catalogue number: 89200005
Issue number: 2020004
Release date: February 17, 2020
QGIS Demo 4
Interacting with data in the Map Canvas - Video transcript
(The Statistics Canada symbol and Canada wordmark appear on screen with the title: "Demo 4 - Interacting with data in the Map Canvas")
Now that we have learned to load and order our datasets in QGIS, let’s explore some tools for interacting with them in the Map Canvas, particularly those found on the Map Navigation and Attribute toolbars. The skills covered today will provide skills for changing and saving the extent, as well as identifying and selecting features from layers in the Map Canvas.
So picking up where we left off…
The Map Navigation toolbar contains tools for changing the scale of the Canvas. By default the Pan Map tool is engaged. Simply left-click and drag the Canvas in the direction of interest.
The Zoom Tools operate similarly, left-click and drag across the area you’d like to zoom to. Depending upon the size of the box that’s drawn determines how much the scale changes. So if we draw a large box the change is negligible, whereas a smaller box the change is much more substantial. Alternatively you can use the scroll-bar of your mouse, scrolling backward and forward to zoom out and in respectively.
If we want to return to the extent of all active layers in the Panel we can use the Zoom to Full tool – helpful when we can’t find a particular dataset or if we just want to return to the full extent.
The Zoom to Layer tool is useful when the extents of loaded datasets differ
and works on the selected layer in the Layers Panel. Applying it to the road segments layer, it zooms to Manitoba, the area for which we downloaded the dataset.
The Zoom Last and Next tools are effectively the Undo and Redo of changes in the Canvas, enabling us to scroll through our previous zooms.
If you are going to be focussing on one area quite a lot for analysis or visualization, you can add a Spatial Bookmark and provide the bookmark with a name. Then if we were to close the Panel and zoom to another area in the map canvas, we can reopen the Panel, select the bookmark and the zoom icon to return to the saved extent.
Just before moving on to the Attribute Toolbar lets discuss grouping layers. We can use the Shift and Control keys to create a selection of layers, then right-click and hit Group Selected. This has many applications such as grouping thematically related layers, preparing mapping groups or organizing datasets such as toggling off many layers at once. Within the group, individual layers can be toggled off and on as normal. We can also right-click to Move a layer out of the Group or drag and drop – as desired.
Now on to the Attribute toolbar – which as the name suggests contains various tools for selecting, editing and examining the attributes of active layers in the Layers Panel. Today we’ll use the Interactive Selection and Identify tools, which default to the selected layer in the Layers Panel.
So with the Census Division layer selected, we can zoom in and left-click to select individual features. We can also drag across to select multiple features. Using Control we can add and remove individual features, or remove a selection of features. Alternatively we can use Shift to add many features to the selection. We can click the Deselect Icon on the toolbar to remove the selection.
If we expand the drop-down there are alternative selection options:
Select by Polygon is helpful for selecting irregular shaped features. We can left-click to add individual vertices and right-click to complete the polygon.
There is also Select by Radius, where we can zoom in, left-click a point of interest and left-click again when satisfied with the radius. Alternatively, we can specify the radius value in the top-right corner.
The Identify tool operates in a similar fashion. We can click an individual feature, and as we can see the Identify Panel returns information on both the geometry and attributes of the identified feature. Similar to the Interactive Selection tools we can drag across to identify multiple features and use the Collapse and Expand All icons to rapidly examine their attributes. Re-enabling the Census Subdivision layer, we can right-click and select Identify All. Here we returned two division features and six census subdivision features.
The same options from the interactive selection tool are available in the Identify tool by expanding the drop-down icon in top-centre of the Panel. Additionally we can change the Mode to alter which layers features are returned by the tool. Changing from Current to Top-Down will identify from all active layers. So re-enabling our grouped layers and creating a small selection in Northern Ontario we’ve identified a few features within the hydrological layer and ultimately returned features from three separate layers.
To remove the identified features click the Clear Results icon within the Identify Panel.
So that summarizes some of the basic tools for changing the extent and scale of the map canvas as well as interacting with vector datasets in the map canvas. In the next demo we will explore additional information found within the Attribute table and Layer Properties box of vector datasets.
(Canada wordmark appears.)