It is possible to define the parameters, in Cartes & Données, of the outlines of the road base maps in order to make these later look like the roads of a classical atlas.
First, add the motorway base map to your diagram. Link your base map to a “grey motorway outlines” module. Then link this outlines module to displaying.
Open the parameters of the « outlines » module by double-clicking on it, then modify the color choosing a dark grey, and the thickness (this later depends on the scale with which you are working: entire France, region or province. Here, we have chosen a thickness of 1,5 km for the province of Hérault).
Add a second outlines module in the diagram (or duplicate the previous one with CTRL+C, CTRL+V) and rename it « red motorway outlines ». Then link this second outlines module to displaying.
Open the parameters of the outlines module by double-clicking on it, then modify the color, choosing a shade of darker or clearer red, and a thickness slightly finer than the outline of the grey outline (here, we have entered a 1 kilometer thickness).
You can also realize the same operation with a second road base map, watching over to adapt the thickness and the color.
|Grey outlines for roads||Orange outlines for roads|
In your displaying module, you can modify the order of appearance of the layers in order to make the motorways appear above or below the roads upon your convenience.
Final result :