Display credit in map composer? [duplicate]

Question

I am trying to publish maps from QGIS Map Composer.

I would like to automatically add the credits of the background layers displayed in the composition (like OSM, Bing, ...)

I am aware of such a feature in main QGIS window using View -> Decorations -> Copyright label but

• this data is not shown in composer
• I am looking for an expression to adapt the text depending of the active layer

(Currently using either qgis 2.18 or 3.4)

Answer 1

Please read everything, there are some updates starting from QGIS 3.4 to QGIS 3.18.

In QGIS 3.4, you can build your attribution label automatically, according to layers which are visible.

First, you need to setup metadata for all your layers.

In QGIS 3.4.0 or 3.4.4, you had to use the QGIS Server panel and fill the attribution field:

Since QGIS 3.4.5, you can use the Metadata panel:

In my project, I have 3 layers, but 2 layers have the same attribution Provider 2.

Then, in your layout, give an itemID to your map:

Then, in your label, you can create an expression like this:

array_to_string( -- 4 we make the attribution list unique and convert to string
    array_distinct(
        array_foreach( --2 for each layer in the map1
            map_get(item_variables('map1'),'map_layers')  --1 get the list of layers in the map1
            ,array_to_string(
                -- 3 we fetch the attribution for the layer
                layer_property(@element,'attribution')))))

Try to understand the expression by reading comments from 1 to 4.

This will render the correct attribution based on layers which are visible in my map. It will also remove attributions which are the same across layers.

In QGIS 3.6.0, you can add the array_sort expression to sort alphabetically.

In QGIS 3.18, there is now a map_credits( 'Main Map' ) expression function which does all the array_foreach, layer_properties etc ... !

Answer 2

One answer to your question can be a union of the great answers (in fact, your question is almost a duplicate) of this one: Automating citation of data source in QGIS print composer?

• Add a new text label to the layout.

• In the item properties of the label, main properties, click on Insert an Expression.

• In the expression builder, switch to the Function Editor tab, and paste this code:

# Be sure to import iface from qgis.utils

from qgis.core import *
from qgis.gui import *
from qgis.utils import iface

@qgsfunction(args='auto', group='Custom')
def get_layer_name(feature, parent):
    return qgis.utils.iface.activeLayer().name()  

Its define a new get_layer_name() function that returns the name of the active layer and can be found under the Custom group of the expressions list.

• Click on Save and Load Function.

• Switch to the Expression tab and write this expression:

layer_property( get_layer_name(), 'attribution')

It returns the Attribution metadata of the active layer.

Don't forget to refresh the layout view when the active layer has changed.