An important concept in KLayout are the layer views. KLayout displays the layers of a layout by default in a list on the right side of the main window. This list however, does not directly reflect the layers in the layout database. Instead this list is a collection of "views". A view is a description of what is to be displayed and how.
Essentially, the entries in the layer list are pointers to layers in the database, together with a description how to paint the shapes on these layers (the "layer properties").
The pointer is the "source" of a layer view. This is typically a GDS layer and datatype, but can be a layer name (for DXF for example). There are also abstract sources (such as cell boundaries) and the sources can include selectors or modifiers. Selectors are used to only display shapes with certain user properties or from certain hierarchy levels. Modifiers transform the shapes before they are drawn for example. The source is defined by a "source specification" - this is a string describing the database layer and selectors and modifiers. A simple source string is "1/0" which is for GDS layer 1, datatype 0 without and selectors or modifiers. To change the source, use "Change Source" from the layer list's context menu.
See Transforming Views And Property Selectors for some source specification string applications and more details.
Beside the source, a layer entry has a display name. This is an arbitrary text providing a description for the user. By default - when no such name is present - the source of the layer will be displayed. To change the display name, use "Rename" from the layer list's context menu.
Plus of course, the layer views have many options to specify the drawing style, animations and decorations.
The concept of separating views from the database layers opens some interesting options:
The concept on the other hand is slightly counter-intuitive at first. Here are some hints: