Data Visualizing is becoming an important research topic in computer science, and has received considerable attention in the last two decades. In several instances, visualization is a crucial step in order to easily access and properly understand the data. With it, the analysis and the decision making is a relatively easier task. In this book, we will focus on the visualization of the concept hierarchies by producing several geometric representations. The main tools used are the graphs where the concepts are represented by vertices and the edges represent the relationships between concepts. We consider many aesthetic criteria that fit our specific application: the levels should be kept together as much as possible, the drawing area should be as small as possible, the number of crossings should be minimized, etc. Also, we will develop a decomposition technique that will be very useful in many instances.