The Geo-Wiki Project is a citizen science network that hopes to improve the overall quality of land use and land cover maps across the globe. They host a variety of projects, all of which use their online Google Earth Application to enlist citizen scientists to improve spatial data. By comparing global land use and land cover data to the aerial photography that appears in Google Earth, you can help improve the validity of important data that is being used to solve important global problems.
Geo-Wiki supports a variety of projects that tackle issues that include climate change, the bio-diversity of plants, and the viability of changing agriculture.
They even have developed mobile apps that allow you to ‘ground truth’ data by adding your own photographs of what’s near you.