Extremely rich and diverse knowledge about places across the world is available online in a variety of forms, including structured data, image, and natural language description. Map-based exploration of this knowledge has potential to aid a number of applications from education to marketing. In this presentation we describe a system to map geographic regions associated with arbitrary keywords, phrases, and texts by computing topic surfaces over the Earth from unstructured natural language text. Our methodology combines natural language processing and geostatistics and is built using freely available open source tools. We train our system on Wikipedia and travel blog entries and demonstrate it with a general-purpose geographic knowledge exploration tool.