3.2. Lesson: Labels

Os rótulos podem ser adicionados a um mapa para mostrar qualquer informação sobre um objeto. Qualquer camada vetorial pode ter rótulos associados. Esses rótulos tem seu conteúdo baseado nos atributos de uma camada.

O objetivo desta lição: Aplicar rótulos úteis e bonitos para uma camada.

3.2.1. basic Follow Along: Utilizando Rótulos

First, ensure that the labeling button is visible in the GUI:

  1. Go to the menu item View ‣ Toolbars

  2. Ensure that the Label Toolbar item has a check mark next to it. If it doesn’t, click on the Label Toolbar item to activate it.

  3. Click on the places layer in the Layers panel so that it is highlighted

  4. Click on the labeling toolbar button to open the Labels tab of the Layer Styling panel

  5. Switch from No Labels to labeling Single Labels

    You’ll need to choose which field in the attributes will be used for the labels. In the previous lesson, you decided that the name field was the most suitable one for this purpose.

  6. Select name from the Value list:

    ../../../_images/select_label_with.png
  7. Clique em Aplicar

Agora o mapa deve ter etiquetas como estas:

../../../_images/first_place_names.png

3.2.2. basic Follow Along: Alterando as opções de Rótulo

Depending on the styles you chose for your map in earlier lessons, you might find that the labels are not appropriately formatted and either overlap or are too far away from their point markers.

Nota

Above, you used the labeling button in the Label Toolbar to open the Layer Styling panel. As with Symbology, the same label options are available via both the Layer Styling panel and the Layer Properties dialog. Here, you’ll use the Layer Properties dialog.

  1. Open the Layer Properties dialog by double-clicking on the places layer

  2. Select the labeling Labels tab

  3. Assegure-se que a opção Texto está selecionada na lista de opções do lado esquerdo, depois, atualize as opções de formato de texto para que coincida com o que é mostrado aqui:

    ../../../_images/label_formatting_options.png
  4. Clique em Aplicar

    That font may be larger and more familiar to users, but its readability is still dependent on what layers are rendered beneath it. To solve this, let’s take a look at the Buffer option.

  5. Select Buffer from the left-hand options list

  6. Selecione a opção Desenhar buffer do texto, depois escolha as opções que coincidem com o que se mostra aqui:

    ../../../_images/buffer_options.png
  7. Clique em Aplicar

    Você verá que isso adiciona um buffer ou borda colorida aos rótulos de places, tornando-os mais fáceis de ver no mapa:

    ../../../_images/buffer_results.png

    Agora, podemos resolver o posicionamento dos rótulos em relação aos seus pontos.

  8. Select Placement from the left-hand options list

  9. Select Around point and change the value of Distance to 2.0 Millimeters:

    ../../../_images/offset_placement_settings.png
  10. Clique em Aplicar

    Você verá que os rótulos já não estão sobrepostos aos pontos.

3.2.3. moderate Follow Along: Utilizando Rótulos no lugar da Simbologia da Camada

In many cases, the location of a point doesn’t need to be very specific. For example, most of the points in the places layer refer to entire towns or suburbs, and the specific point associated with such features is not that specific on a large scale. In fact, giving a point that is too specific is often confusing for someone reading a map.

Para citar um exemplo: em um mapa do mundo o ponto dado para a União Europeia pode estar em algum lugar na Polônia. Para alguém lendo o mapa, ver um ponto marcado União Europeia na Polônia, pode levar a crer que a capital da União Europeia é na Polônia.

Então, para evitar esse tipo de mal-entendido, muitas vezes é útil desativar os símbolos de pontos e substituí-los por completo com rótulos.

No QGIS, você pode fazer isso alterando a posição dos rótulos a serem apresentados diretamente sobre os pontos a que se referem.

  1. Open the labeling Labels tab of the Layer Properties dialog for the places layer

  2. Select the Placement option from the options list

  3. Click on the Offset from point button

    Isso revelará as opções para Quadrante que você pode usar para definir a posição do rótulo em relação ao ponto. Neste caso, queremos que o rótulo esteja centralizado no ponto, então, escolha o quadrante central:

    ../../../_images/quadrant_offset_options.png
  4. Hide the point symbols by editing the layer Symbology as usual, and setting the size of the Marker size to 0.0:

    ../../../_images/hide_point_marker.png
  5. Click Apply and you’ll see this result:

    ../../../_images/hide_point_marker_results.png

If you were to zoom out on the map, you would see that some of the labels disappear at larger scales to avoid overlapping. Sometimes this is what you want when dealing with datasets that have many points, but at other times you will lose useful information this way. There is another possibility for handling cases like this, which we’ll cover in a later exercise in this lesson. For now, zoom out and click on the showUnplacedLabel button in the toolbar and see what happens.

3.2.4. moderate Try Yourself Personalizar Rótulos

  • Reset the label and symbol settings to have a point marker and a label offset of 2.0 Millimeters.

Verifique seus resultados

  • Set the map to the scale 1:100000. You can do this by typing it into the Scale box in the Status Bar. Modify your labels to be suitable for viewing at this scale.

Confira seus resultados

3.2.5. moderate Follow Along: Rotulando Linhas

Agora que você sabe como funciona a rotulagem, há um problema adicional. Pontos e polígonos são fáceis de rotular, mas o que dizer sobre linhas? Se você as rotulasse da mesma forma que os pontos, o resultado ficaria assim:

../../../_images/bad_street_labels.png

We will now reformat the roads layer labels so that they are easy to understand.

  1. Hide the places layer so that it doesn’t distract you

  2. Activate labeling Single Labels for the roads layer as you did above for places

  3. Set the font Size to 10 so that you can see more labels

  4. Zoom in on the Swellendam town area

  5. In the Labels tab’s Placement tab, choose the following settings:

    ../../../_images/street_label_settings.png

    You’ll probably find that the text styling has used default values and the labels are consequently very hard to read. Update the Text to use a dark-grey or black Color and the Buffer to use a light-yellow Color.

    O mapa ficará parecido com esse, dependendo da escala:

    ../../../_images/street_label_formatted.png

    Verá que alguns dos nomes das ruas aparecem mais de uma vez e que nem sempre são necessários. Para prevenir isso:

  6. In the Labels tab of the Layer Properties dialog, choose the Rendering option and select Merge connected lines to avoid duplicate labels as shown:

    ../../../_images/merge_lines_option.png
  7. Clique OK.

    Outra função útil é uma que previne que rótulos sejam desenhados para feições muito pequenas, difíceis de serem notadas.

  8. In the same Rendering panel, set the value of Suppress labeling of features smaller than … to 5.00 mm and note the results when you click Apply

    Try out different Placement settings as well. As we’ve seen before, the Horizontal option is not a good idea in this case, so let’s try the Curved option instead.

  9. Select the Curved option in the Placement panel of the Layers tab

Aqui está o resultado:

../../../_images/final_street_labels.png

As you can see, this hides some labels that were previously visible, because of the difficulty of making some of them follow twisting street lines while still being legible. It makes other labels much more useful since they track the roads rather than float in space between them. You can decide which of these options to use, depending on what you think seems more useful or what looks better.

3.2.6. hard Follow Along: Ajustes Definidos de Datos

  1. Deactivate labeling for the roads layer

  2. Reactivate labeling for the places layer

  3. Open the attribute table for places via the openTable button

    It has one field which is of interest to us now: place which defines the type of urban area for each record. We can use this data to influence the label styles.

  4. Navigate to the Text panel in the places Labels panel

  5. Click the dataDefined button next to the Italic text button beneath Style and select Edit… to open the Expression String Builder:

    ../../../_images/expression_string_builder.png
  6. Under Fields and Values, double click on place and then click All Unique. This will list all unique values of the place field of this layer. Add a = in the text editor and then double click on town.

    Alternatively, you can type: "place" = 'town' directly in the text editor.

  7. Click OK twice:

    ../../../_images/expression_builder_settings.png

Notice that the labels for all places whose place field matches town are displayed in italics.

../../../_images/italic_label_result.png

3.2.7. hard Try Yourself Utilizando Ajustes Definidos de Datos

Nota

Estamos saltando hacia adelante un poco para demostrar algunos ajustes avanzados de las etiquetas. En el nivel avanzado, se asume que sabrás qué significa lo siguiente. En caso contrario, eres libre de dejar esta sección y volver cuando hayas cubierto los materiales requeridos.

  1. Open the Attribute Table for places

  2. Enter edit mode by clicking the toggleEditing button

  3. Adicionar uma nova coluna com o botão newAttribute

  4. Configúrala como esta:

    ../../../_images/font_size_column.png
  5. Use this to set custom font sizes for each different type of place (each key in the place field)

Comprueba tus resultados

3.2.8. hard Más Posibilidades Con Etiquetas

We can’t cover every option in this course, but be aware that the Label tab has many other useful functions. You can set scale-based rendering, alter the rendering priority for labels in a layer, and set every label option using layer attributes. You can even set the rotation, XY position, and other properties of a label (if you have attribute fields allocated for the purpose), then edit these properties using the tools adjacent to the main Layer Labeling Options button:

labeling showPinnedLabels pinLabels showHideLabels moveLabel rotateLabel changeLabelProperties

(Estas herramientas estarán activas si los campos de atributo requeridos están disponibles y el modo edición está activado.)

Eres libre de explorar más posibilidades del sistema de etiquetas.

3.2.9. In Conclusion

Has aprendido a usar la capa de atributos para crear etiquetas dinámicas. Esto puede hacer tu mapa mucho más informativo y estilizado.

3.2.10. What’s Next?

Ahora que sabes cómo los atributos conllevan una diferencia visual en tu mapa, ¿Como los usamos para cambiar la simbología de los objetos? ¡Ese es el tema de la siguiente lección!