Walter Christaller was a German geographer known for developing the Central Place Theory in 1933. His work has greatly influenced urban geography and regional science.
Geography: The study of places and the relationships between people and their environments.
Urban Geography: The sub-discipline of geography which concentrates on those parts of Earth's surface that have a high concentration of buildings and infrastructure.
Regional Science: A field of the social sciences concerned with analytical approaches to problems that are specifically urban, rural, or regional.