3.1. Lesson: Trabalhando com Dados Vetoriais

Vector data is arguably the most common kind of data you will find in the daily use of GIS. The vector model represents the location and shape of geographic features using points, lines and polygons (and for 3D data also surfaces and volumes), while their other properties are included as attributes (often presented as a table in QGIS). It is usually used to store discrete features, like roads and city blocks. The objects in a vector dataset are called features, and contain data that describe their location and properties.

Meta para esta lição: Aprender mais sobre a estrutura de dados vetoriais e como carregar conjuntos de dados vetoriais em um mapa.

3.1.1. Follow Along: Visualizando Atributos da Camada

É importante saber que os dados que você estará trabalhando não representam apenas onde os objetos estão no espaço, mas também te diz o que esses objetos são.

From the previous exercise, you should have the rivers layer loaded in your map. The lines that you can see right now are merely the position of the rivers: this is the spatial data.

To see all the available data in the rivers layer, select it in the Layers panel and click the button.

It will show you a table with more data about the rivers layer. This is the layer’s Attribute table. A row is called a record, and represents a river feature. A column is called a field, and represents a property of the river. Cells show attributes.

Essas definições são comumente usadas ​​em SIG, por isso é essencial lembrá-las!

Agora você pode fechar a tabela de atributos.

3.1.2. Try Yourself Exploring Vector Data Attributes

1. How many fields are available in the rivers layer?

2. Tell us a bit about the town places in your dataset.

Check your results

3.1.3. Follow Along: Loading Vector Data From GeoPackage Database

Databases allow you to store a large volume of associated data in one file. You may already be familiar with a database management system (DBMS) such as Libreoffice Base or MS Access. GIS applications can also make use of databases. GIS-specific DBMSes (such as PostGIS) have extra functions, because they need to handle spatial data.

The GeoPackage open format is a container that allows you to store GIS data (layers) in a single file. Unlike the ESRI Shapefile format (e.g. the protected_areas.shp dataset you loaded earlier), a single GeoPackage file can contain various data (both vector and raster data) in different coordinate reference systems, as well as tables without spatial information; all these features allow you to share data easily and avoid file duplication.

In order to load a layer from a GeoPackage, you will first need to create the connection to it:

1. Click on the ^{Open Data Source Manager} button.

2. On the left click on the GeoPackage tab.

3. Click on the New button and browse to the training_data.gpkg file in the exercise_data folder you downloaded before.

4. Select the file and press Open. The file path is now added to the Geopackage connections list, and appears in the drop-down menu.

You are now ready to add any layer from this GeoPackage to QGIS.

1. Click on the Connect button. In the central part of the window you should now see the list of all the layers contained in the GeoPackage file.

2. Select the roads layer and click on the Add button.

   

   A roads layer is added to the Layers panel with features displayed on the map canvas.

3. Click on Close.

Congratulations! You have loaded the first layer from a GeoPackage.

3.1.4. Follow Along: Loading Vector Data From a SpatiaLite Database with the Browser

QGIS provides access to many other database formats. Like GeoPackage, the SpatiaLite database format is an extension of the SQLite library. And adding a layer from a SpatiaLite provider follows the same rules as described above: Create the connection –> Enable it –> Add the layer(s).

While this is one way to add SpatiaLite data to your map, let’s explore another powerful way to add data: the Browser.

1. Click the icon to open the Data Source Manager window.

2. Click on the Browser tab.

3. In this tab you can see all the storage disks connected to your computer as well as entries for most of the tabs in the left. These allow quick access to connected databases or folders.

   For example, click on the drop-down icon next to the GeoPackage entry. You’ll see the training-data.gpkg file we previously connected to (and its layers, if expanded).

4. Right-click the SpatiaLite entry and select New Connection….

5. Navigate to the exercise_data folder, select the landuse.sqlite file and click Open.

   Notice that a landuse.sqlite entry has been added under the SpatiaLite one.

6. Expand the landuse.sqlite entry.

7. Double-click the landuse layer or select and drag-and-drop it onto the map canvas. A new layer is added to the Layers panel and its features are displayed on the map canvas.

   
   
   

Dica

Enable the Browser panel in View ‣ Panels ‣ and use it to add your data. It’s a handy shortcut for the Data Source Manager ‣ Browser tab, with the same functionality.

Nota

Remember to save your project frequently! The project file doesn’t contain any of the data itself, but it remembers which layers you loaded into your map.

3.1.5. Try Yourself Load More Vector Data

Load the following datasets from the exercise_data folder into your map using any of the methods explained above:

• buildings

• water

Check your results

3.1.6. Follow Along: Reordenando as Camadas

As camadas na lista de Camadas são desenhadas no mapa em uma determinada ordem. A camada mais abaixo na lista é desenhada em primeiro lugar e a camada na parte superior é desenhada por último. Alterando a ordem em que são mostradas na lista, você alterará a ordem em que elas são desenhadas.

Nota

You can alter this behavior using the Control rendering order checkbox beneath the Layer Order panel. We will however not discuss this feature yet.

A ordem em que as camadas estão carregadas no mapa está provavelmente sem lógica nesta etapa. É possível que a camada road (via) esteja completamente escondida por que outras camadas estão sobre ela.

Por exemplo, esta ordem de camada…

… would result in roads and places being hidden as they run underneath the polygons of the landuse layer.

Para resolver este problema:

1. Clique e arraste em uma camada na lista Camadas.

2. Reordene-os para se parecer com isso:

Você verá que o mapa agora faz mais sentido visualmente, com estradas e edifícios que aparecem acima das regiões de uso da terra.

3.1.7. In Conclusion

Agora você adicionou todas as camadas que precisa de várias fontes diferentes.

3.1.8. What’s Next?

Usando cores aleatórias atribuídas automaticamente ao carregar as camadas, o seu mapa atual possivelmente não será fácil de ler. Seria preferível atribuir sua própria escolha de cores e símbolos. Isto é o que você vai aprender a fazer na próxima lição.