Use queries and filters

A query in relation to GIS is the information that you put into your GPS or computer with a Query on what area you would like to get directions to or view.

Manipulate views of data

This technique reduces multidimensional data by allowing the visitor to choose only the dimensions of interest. Dynamic queries let the user change his or her view in real time.

Break down the data into simpler categories, such as streets, highways, demographics, and housing density. The user can toggle these categories on and off, to compare what interests them.

http://www.idea.org/page69.html

Layers

This picture also shows how the layers in GIS work


http://www.mapcruzin.com/what-is-gis.htm

What is GIS?

Here is a short video that i have used to show how the layers of GIS work, although there is no actual narration on the subject of layers the small section of the video that starts at 0.20 and ends at 0.32 shows visually how the layers work

http://www.youtube.com/watch?v=kEaMzPo1Q7Q