The massive open online course (MOOC) is a new approach for teaching online. MOOCs stand apart from traditional online classes in that they support thousands of learners through content and assessment mechanisms that can scale. A reason for their size is that MOOCs are free for anyone to take. Here we describe the design, development, and teaching of a MOOC called "Maps and the Geospatial Revolution." We explore the geography of the student population, the experience of teaching a MOOC, and evaluate its impacts on learning. We conclude with several key challenges and opportunities we see for MOOCs in geography.