Everybody (from a single individual to a whole city or country) has an impact on the earth because they consume the products and services of nature. Their ecological impact corresponds to the amount of nature they occupy in order to live.
The ecological footprint (or eco-footprint for short) is a tool to measure our ecological performance. It tracks how much individuals, organizations, cities, regions and nations, or humanity as a whole consumes and compares this amount to the resources nature can provide. More precisely, it shows how much biologically productive land and water area a given population occupies to produce all the resources it consumes and to absorb its waste, using prevailing technology
April 22 is Earth Day, how about taking 10 minutes to find out your own personal "ecological footprint"
http://www.myfootprint.org/