If you sit in front a long list of information, it is often difficult to make quickly sense of it. If you look at a map of the same data, you might get a picture of it rather quickly.
1,470,000 US gallons of oil were leaking from an oil pipe of British Petrol in the Gulf of Mexico everyday. What does that tell you? When you look at this map from ifitweremyhome.com, then you get a better sense of it. The oil spill size was as big as Southern UK.
If you do have some data, you can start working with a new great tool called openheatmap.com, however if not, then you need to collect it yourself. One way is done by the grassrootmapping.org project, which has done a great initiative to document the oil spill on the coast line. Another one is the Oil Reporter from the Crisis Commons group. You "only" need an Iphone or Android driven phone and you can get the app to report where oil is found.
Context is king and therefore some other projects want you to share information to find out more about your environment. One example is the Urban Forest Map project: "The Urban Forest Map is a collaboration of government, nonprofits, businesses and you to build an inventory of San Francisco's urban forest." Citizens create an inventory of trees in their city and get exact information about the ecological impact.
Another mapping & crowdsourcing project is a research project, which founds to create a location based happiness index. Through an application, volunters are asked throughout the day about their mood and that information plus the location is then collected. Mappiness shall help to understand "how people's feelings are affected by features of their current environment—things like air pollution, noise, and green spaces."