You can find data sets in a number of places:
Not sure where to begin? Search for your topic in USA.gov-
When you are just getting started, your data gathering is a combination of figuring out what the “interesting questions” are – what area can you solve or provide clarity to by adding GIS data—and what data is readily available.
In the comic to the left, you can see an example of an “interesting question” being asked – “Can we map the photos of birds people take in National Parks and identify them?”
The location data to map photos is readily available, but the image recognition is not available, even though these two pieces of data are connected in the question.
So for your projects, it is a good idea to search with intention, but also remain flexible so that you can create a useful map with the data readily available to you-- you might end up changing focus slightly as you search, and that's OK.
Munroe, R. (n.d.) Tasks. [comic]. Retrieved from http://xkcd.com/1425/.
ESRI is an international supplier of Geographic Information System software, web GIS and geodatabase management applications. They also offer GIS-related information on their website, such as case studies in a variety of areas.
As another option, you can often find case study examples from the news items or reports provided by US government agencies responsible for overseeing resources of regulations in the field you are interested in. Search USA.gov for reports (you can enter a general keyword phrase like "sea level change") or by agency: