We know about the world through our senses. Data feeds our senses. Data are evidence of reality. But data alone are not sufficient. Data shall inform us. Data shall provide actionable knowledge. Proper data design can facilitate this very process, by turning data into information. In the past the main challenge was to get data in the first place. The world was mainly analog, not digital, collecting data was expensive and cumbersome, and people were reluctant to provide data. In recent years this situation has dramatically changed. The data explosion — fueled by digital communication technologies such as the Internet, smart phones, and the emerging Internet of Things — has produced a world of data abundance. Now the challenge is making sense of data rather than generating data. Making sense of data is an analytical challenge and a visualization challenge. This book focuses on the visualization challenge. The most comprehensive and up-to-date book on data visualization.