Certain fields of study tend to cover many of the same topics. Many times, the two fields go hand-in-hand. Electrical engineering, for example, ties tightly with computer science. Same thing between education and sociology. Daniel Ramage and Jason Chuang of Stanford University explore these similarities through the language used in their school's dissertations.
Topic distance is explored between departments from 1993 to 2008. Select a department and it goes to the middle of the circle. Departments with dissertations that were similar for the year are highlighted and near closer. The closer to the center, the more similar. Alternatively, you should also be able to find departments who are fairly different from the rest.
You can also use the time slider on the bottom to check out how some departments grow closer to another over time.
Apparently there were some strong similarities between the communication dissertations and the one from applied earth sciences. Who knew? [PhD Dissertation Browser]