The term GIS is very closely associated with the layer concept, as a standard GIS will allow you to work in various levels and their proper representation. When you talk about GIS, you will might need to visualize this layer principle. Here is a template for such a visualization you can use under the CC license:
![Layers in a GIS: This shows a digital terrain model, above the distance to the nearest water source, the slope and the TPI.](https://farm8.staticflickr.com/7222/7168721827_dce790e6d1.jpg)