Catalogue number: Catalogue number: 89200005
Issue number: 2020005
Release date: February 17, 2020
QGIS Demo 5
Exploring the Attribute Table and Layer Properties Box of Vector Data - Video transcript
(The Statistics Canada symbol and Canada wordmark appear on screen with the title: "Demo 5 - Exploring the Attribute Table and Layer Properties Box of Vector Data")
Following up from interacting with datasets in the Map Canvas, today we'll explore additional information and parameters found in the Attribute Table and Layer Properties Box. The Attribute Table contains additional variables for analyzing and visualizing vector data, while the Layer Properties box contains tabs that summarize information and provide additional functions. We'll quickly summarize some of the key tabs, their content and use, which we'll cover in detail in later demos.
So to open the Attribute Table of a layer, we can left-click it in the Layers panel and select the Attribute table icon, or right-click the layer and select Open Attribute Table.
So within the table, each column reports an additional variable tied to the vector dataset. These are referred to as fields within GIS, whereas each row corresponds to a specific feature or geometry within the canvas.
Using the tabs on the left-hand side we can select features. With an individual feature selected, we can right-click and Zoom to the Feature, and if we still couldn't see it we could also flash the feature. In this case we can't see our feature as it's hidden by our Census Subdivision layer.
Like the Interactive Selection tools, we can use Shift and Control to select multiple features. Using shift to select features within a range and Ctrl to add individual features. In conjunction, selecting features both within and between ranges. We could also then zoom to our selection. So as you can see, when features are selected in the Attribute Table they are also highlighted in the Canvas and vice-versa – highlighted in yellow in the Canvas and blue in the Attribute Table.
To sort a field, ascending or descending we can left-click once or twice on the field name as needed. This can help select features by specific criteria of interest such as selecting all features within a particular province in this case. We can then also zoom once more and using the Invert feature selection, we can switch the selection of features.
To move selections to the top of the attribute table, we can click the Move Selection to Top icon. So now if we add any additional features to our selection they are by default loaded at the top of the table. We could also copy our information and paste it into an external spreadsheet editor for further analysis.
Expanding the Show All Features dropdown, we could apply a field filter, selecting the field to filter by and specific criteria to use in filtering the table. Subsequently, the only remaining entries are those that satisfy the entered criteria, in this case Province name being Manitoba.
If we want a dynamic representation of our attribute features based on the scale and extent, we can apply a Show Features Visible on Map. Now if we change the scale or change the location, our table is filtered accordingly.
To enable additional tools we can enable the editor. This enables us to add or delete features, as well as add and delete fields. We can also click on an individual cell's content to edit its information, or for a selection of features we can use the Update Field Bar, specifying the field to update and the new attributes to update to – in this case clicking Update Selected. If we wanted to retain these changes we can save them, but in this case – since we want to keep our attribute table uniform - we'll just discard the changes and clear our selection.
To open the Layer Properties box of a layer we can right-click it and select Properties or simply double-left click within the Layers Panel.
The Layer Properties box contains various tabs which both summarize information and provide additional functions.
The Information tab summarizes the spatial characteristics as well as some of the attribute information within a dataset.
In the Source Tab we can rename a layer as we did with the Census Subdivisions. We can also use the Query Builder to filter features. However, this would filter the geometries of the layer in the Canvas as opposed to the table when using the Field Filter earlier.
The following four tabs are for visualization. We'll explore the Symbology and Labels tab in an upcoming demo, where we can apply different symbology styles to visualize fields within the attribute table, as well as differing labelling schemes. We can create Diagrams with the attribute information and, when enabled, also apply 3D visualizations.
The Source Fields tab provides more information on the Field Names, Types and additional parameters and with editor enabled we can add or delete a field, as well as rename a field.
So the Joins tab enables you to link datasets together – tables or vectors, by a field with common entries. The tab specifically works for one-to-one joins. So for example, here we could join the Census division and Subdivision layers using the unique Census Division identifier field. If we want to remove our join, simply select it and click the minus icon.
The final tab I'd like to cover is the rendering tab where we can apply a scale-dependent visibility, defining the minimum and maximum scale at which a dataset should begin or suspend rendering. We can set the scale from the drop-downs or set it to the current map canvas scale by clicking on this icon. This is helpful for large or highly detailed datasets that take a long time to render. Now, clicking OK, if we zoom in – our layer remains visible, but zooming out beyond the specified scale, you can see rendering is suspended.
Congratulations everyone! Today you've learned key skills in exploring, selecting and filtering features within the attribute table, performing simple edits and the use of some tabs within the Layer Properties box. In the next demo, we'll cover procedures for creating vector datasets, which includes delineating features and populating their attributes.
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