Rule-based symbology is a powerful feature in QGIS that allows you to customize the appearance of your vector layers based on logical expressions. You can use rule-based symbology to create thematic maps, highlight specific features, or apply conditional formatting. In this article, you will learn how to create and apply rule-based symbology in QGIS in six easy steps.
To start, you need to load your vector layer into QGIS. You can do this by clicking on the Add Vector Layer button on the toolbar, browsing to your file location, and selecting the layer you want to work with. Alternatively, you can drag and drop your vector layer from the file manager into the QGIS canvas.
Next, you need to open the layer properties dialog for your vector layer. You can do this by right-clicking on the layer name in the Layers panel and choosing Properties. Alternatively, you can double-click on the layer name or select the layer and press Ctrl+Enter.
Uma alternativa mais rápida e fácil de chegar no painel de simbologia do QGIS é apertar a tecla F7 do seu teclado. As altera??es de simbologia feitas nesse painel s?o atualizadas ao vivo no projeto.
In the Layer Properties dialog, navigate to the "Symbology" tab. From the dropdown menu at the top of the dialog, select "Rule-based" symbology. This will allow you to define rules to symbolize different features based on their attributes.
To create a new rule, click on the green plus icon at the bottom of the panel. This will open a dialog where you can define the name, symbol, and filter expression for your rule. You can use any valid QGIS expression to filter your features based on their attributes or geometry. For example, you can use "population" > 1000000 to select features with a population greater than one million. You can also use AND, OR, and NOT operators to combine multiple conditions. You can preview the result of your expression by clicking on the Select button.
Click on the "Add rule" button to create a new rule. Each rule represents a condition that determines how features will be symbolized. For example, you can create a rule to symbolize all features where the "type" attribute equals "forest" with a green color. You can add multiple rules to cover different conditions.
Once you have created your rules, you can apply them to your layer by clicking on OK. You will see your layer styled according to your rules in the QGIS canvas. You can also adjust the order and visibility of your rules by dragging and dropping them in the panel or by using the checkboxes.
If you want to edit or delete your rules, you can do so by right-clicking on the rule name in the panel and choosing Edit Rule or Remove Rule. You can also use the green pencil icon or the red minus icon at the bottom of the panel. To edit or delete multiple rules at once, you can use the Shift or Ctrl keys to select them and then use the buttons or the context menu.