QGis Data Exploration Tutorial
Exploring Data
Exploring data is a fundamental part of working with QGIS. This section will cover how to view, query, and manipulate your data using QGIS tools and features effectively.
1. Opening the Attribute Table
The attribute table provides a detailed view of the data associated with your vector layers. Here's how to access and explore it:
Steps to Open the Attribute Table:
- Right-click on the layer in the Layers Panel.
- Select Open Attribute Table from the context menu.
The attribute table will open in a new window, displaying all attributes and allowing you to perform various actions.
Understanding the Attribute Table
In the attribute table, each row represents a feature, and each column represents an attribute. You can:
- Sort: Click on the column header to sort by that attribute.
- Filter: Use the filter option to display only records that meet specific criteria.
- Edit: Toggle the editing mode to make changes to the attribute values.
2. Using the Identify Features Tool
The Identify Features tool allows you to click on a feature in the map canvas to view its attributes quickly.
How to Use the Identify Features Tool:
- Select the Identify Features tool from the toolbar (an icon that looks like a cursor with a question mark).
- Click on the feature you want to explore in the map canvas.
- A popup will appear, displaying the attributes of that feature.
3. Exploring Data with Filtering
Filtering allows you to focus on specific records in your attribute table. This can be done using the following methods:
3.1 Simple Filter
In the attribute table:
- Click the Show Selected Features button to filter only selected features.
- Use the filter expression dialog by clicking the Filter button.
3.2 Advanced Filtering
For more complex filtering, use the expression builder:
- Open the attribute table, and click on the Advanced Filter button.
- Construct your expression using fields and operators (e.g., "population" > 10000).
- Click OK to apply the filter.
4. Visualization and Symbology
Visual representation of data is essential for effective communication. QGIS allows you to customize the symbology of your layers:
4.1 Changing Layer Symbology
Steps to Change Symbology:
- Right-click on the layer in the Layers Panel and select Properties.
- Navigate to the Symbology tab.
- Select the style type (Single Symbol, Graduated, Categorized, etc.).
- Configure the options based on your data (e.g., colors, size).
- Click OK to apply changes.
4.2 Using Styles
You can save your customized styles for future use:
- In the Layer Properties dialog, navigate to the Style tab.
- Click Save Style to store your current symbology settings.
- Load saved styles in future projects to maintain consistency.