Toggle all layers on or off

[PetersonGIS]

Add functionality to turn all layers on or off at once.

[justenPalmer]

@PetersonGIS, what is the purpose of turning all layers off? Is it to single out a single layer and its style?

[PetersonGIS]

In this particular case I was starting a new style with an old style. So I turned off all the layers to start working on them one at a time. Each layer I modified for the new style I would keep on. The old layers I would keep off as a way of knowing what was still to be done.

To answer your question, yes, this is often a way of isolating a single layer and style. GIS programs usually have a way to change the visibility of selected groups of layers as well as all or nothing.