First I created a placemark for my house, then I added polygons to represent the area that I visit in order to use various services.

Polygons (click image for large version)

Then I used the KML circle generator to create circles based on the maximum distance I am prepared to travel to use a particular service. I centred the circle on the service, and used the Ruler tool to estimate the distance in meters to my house.
The circle colour and width was edited in the Properties dialogue to make them stand out better – the default is a thin red circle.

Circles

During the lesson I started with all the information turned off (apart from my house placemark). I turned on the polygons one by one and facilitated a discussion about convenience / comparison goods, range and threshold population. I then added the circles to demonstrate the concept of sphere of influence.

my life in spheres

The lesson seemed to go very well. Here are the resources I used (neither of which would be relevant to any other school – but feel free to adapt etc)

The original sphere-of-influence Google Earth file

And here’s a worksheet I made for the lesson. (This is a Foundation sheet – more able students were given an edited version.)