18.2.5. The Legend Item

The Legend item is a box or a table that explains the meanings of the symbols used on the map. A legend is then bound to a map item. You can add a legend item with the Add Legend tool following items creation instructions and manipulate it the same way as exposed in Interacting with layout items.

By default, the legend item displays all available layers and can be refined using its Item Properties panel. Other than the items common properties, this feature has the following functionalities (see Рис. 18.25):

Рис. 18.25 Legend Item Properties Panel

18.2.5.1. Main properties

The Main properties group of the legend Item Properties panel provides the following functionalities (see Рис. 18.26):

Рис. 18.26 Legend Main properties group

In Main properties you can:

• Change the Title of the legend. It can be made dynamic using the data-defined override setting, useful for example when generating an atlas;

• Choose which Map item the current legend will refer to. By default, the map over which the legend item is drawn is picked. If none, then it falls back to the reference map.

  Примечание

  Variables of the linked map item (@map_id, @map_scale, @map_extent…) are also accessible from data-defined properties of the legend.

• Wrap the text of the legend on a given character: each time the character appears, it’s replaced with a line break;

• Set the symbols and text placement in the legend: the Arrangement can be Symbols on left or Symbols on right. The default value depends on the locale in use (right-to-left based or not).

• Use Resize to fit contents to control whether or not a legend should be automatically resized to fit its contents. If unchecked, then the legend will never resize and instead just stick to whatever size the user has set. Any content which doesn’t fit the size is cropped out.

18.2.5.2. Legend items

The Legend items group of the legend Item Properties panel provides the following functionalities (see Рис. 18.27):

Рис. 18.27 Legend Items group

• The legend will be updated automatically if Auto update is checked. When Auto update is unchecked this will give you more control over the legend items. All the icons below the legend items list will be activated.

• The legend items window lists all legend items and allows you to change item order, group layers, remove and restore items in the list, edit layer names and add a filter.

  • The item order can be changed using the and buttons or with „drag-and-drop“ functionality. The order can not be changed for WMS legend graphics.

  • Use the button to add a legend group.

  • Use the button to add layers and button to remove groups, layers or symbol classes.

  • The button is used to edit the layer, group name or title. First you need to select the legend item. Double-clicking the item also opens the text box to rename it.

  • The button uses expressions to customize each symbol label of the selected layer (see Data-define the legend labels)

  • The button adds a feature count for each class of vector layer.

  • The ^{Filter legend by expression} helps you filter which of the legend items of a layer will be displayed, i.e. using a layer that has different legend items (e.g., from a rule-based or categorized symbology), you can specify a boolean expression to remove from the legend tree, styles that have no feature satisfying a condition. Note that the features are nevertheless kept and shown in the layout map item.

  While the default behavior of the legend item is to mimic the Layers panel tree, displaying the same groups, layers and classes of symbology, right-click any item offers you options to hide layer’s name or raise it as a group or subgroup. In case you have made some changes to a layer, you can revert them by choosing Reset to defaults from the contextual menu of the legend entry.

  After changing the symbology in the QGIS main window, you can click on Update All to adapt the changes in the legend element of the print layout.

• With the Only show items inside linked map, only the legend items visible in the linked map will be listed in the legend. This tool remains available when Auto-update is active

• While generating an atlas with polygon features, you can filter out legend items that lie outside the current atlas feature. To do that, check the Only show items inside current atlas feature option.

Data-define the legend labels

allows you to add expressions to each symbol label of a given layer. New variables (@symbol_label, @symbol_id and @symbol_count) help you interact with the legend entry.

For example, given a regions layer categorized by its type field, you can append to each class in the legend their number of features and total area, e.g. Borough (3) - 850ha:

1. Select the layer entry in the legend tree

2. Press the button, opening the Expression String Builder dialog

3. Enter the following expression (assuming symbol labels have not been edited):

   concat( @symbol_label,
           ' (', @symbol_count, ') - ',
           round( aggregate(@layer, 'sum', $area, filter:= "type"=@symbol_label)/10000 ),
           'ha'
         )
   

4. Press OK

18.2.5.3. Fonts

The Fonts group of the legend Item Properties panel provides the following functionalities:

Рис. 18.28 Legend Fonts properties

• You can change the font of the legend title, group, subgroup and item (feature) in the legend item using the font selector widget

• For each of these levels you can set the text Alignment: it can be Left (default for left-to-right based locales), Center or Right (default for right-to-left based locales).

• You set the Color of the labels using the color selector widget. The selected color will apply to all the font items in the legend.

18.2.5.4. Columns

Under the Columns group of the legend Item Properties panel, legend items can be arranged over several columns:

• Set the number of columns in the Count field. This value can be made dynamic e.g., following atlas features, legend contents, the frame size…

• Equal column widths sets how legend columns should be adjusted.

• The Split layers option allows a categorized or a graduated layer legend to be divided between columns.

Рис. 18.29 Legend Columns settings

18.2.5.5. Symbol

The Symbol group of the legend Item Properties panel configures the size of symbols displayed next to the legend labels. You can:

• Set the Symbol width and Symbol height

• Set the markers“ Min symbol size and Max symbol size: 0.00mm means there is no value set.

• Draw stroke for raster symbols: this adds an outline to the symbol representing the band color of the raster layer; you can set both the Stroke color and Tickness.

Рис. 18.30 Legend Symbol configuration

18.2.5.6. WMS LegendGraphic and Spacing

The WMS LegendGraphic and Spacing groups of the legend Item Properties panel provide the following functionalities (see Рис. 18.31):

Рис. 18.31 WMS LegendGraphic and Spacing groups

When you have added a WMS layer and you insert a legend item, a request will be sent to the WMS server to provide a WMS legend. This Legend will only be shown if the WMS server provides the GetLegendGraphic capability. The WMS legend content will be provided as a raster image.

WMS LegendGraphic is used to be able to adjust the Legend width and the Legend height of the WMS legend raster image.

Spacing around title, groups, subgroups, symbols, labels, boxes, columns and lines can be customized through this dialog.