In some applications, the layer list will grow very large and keeping track of the important layers may be hard. KLayout provides support for that task in two ways: KLayout checks whether a layer carries any information and displays the layers in a different way in the layer list, if it is empty.
Two ways of checking the information content of a layer are provided: either a layer is said to be empty if the current cell does not have any shapes on it. Alternatively, a layer can be identified to be empty by checking if any shape is shown in the current view (more precisely if any shape's bounding box overlaps with the current view rectangle). The latter mode can be selected in the layer list's context menu with the option "Test For Shapes in View".
If a layer is determined to be empty, it is either grayed out or it is now shown at all. The latter option keeps the layer list short and is selected with "Hide Empty Layers" from the layer list's context menu.