This book aims to show how the Maximum Entropy (MaxEnt) approach has changed deeply the traditional research methods in regional and urban geography as the result of paradigm shifts occurred during the last 50 years. MaxEnt method as pioneered by A. Wilson (1967,1970) and “Spatial Entropy” concept by M. Batty (1974) have been based on the Information Theory that was founded by Shannon (1948), E.T.Jaynes (1957) and Kullback (1959) and others. Information Theory has provided the theoretical foundation for challenging the uncertainty and incomplete information issues concerning the complex urban structure. MaxEnt, as a new logic, aims to assign probabilities “maximally noncommittal” with respect to the missing information. This dissertation applies Spatial Entropy measures to Ankara 1970 and 1990 census data by 34 zones and compares the population density changes during the two decades. This book shall not only guide young generations to understand the past contributions but also encourage them to make further researches under the information-theoric Weltanschauung.