This book is the end result of a thirty-year journey that began at the University of Rochester in 1974. In the spring semester of that year I took a course from Richard McKelvey on scaling methods. That course changed my life. Dick showed us how to take lists of numbers and transform them into simple pictures that conveyed meaning. Summarizing data with pictures! It was a revelation – I knew that this was what I wanted to do as a career.

Everything crystallized for me because the previous academic year I had taken a graduate course with Bill Riker on positive political theory where I learned about spatial voting models. After reading Riker and Ordeshook (1973) and Converse (1964), the scaling course with Dick convinced me that the correct way to measure ideology or Conversian belief systems was through the empirical estimation of spatial models of choice.

Dick left Rochester in the fall of 1974 to visit at Carnegie-Mellon for a year, and then he elected to stay at CMU. Partly due to my persistence but mostly due to his being such a nice guy, Dick agreed to chair my dissertation despite the fact that he had left Rochester. I went down to Pittsburgh two times to work with him before I finished up in late 1977. During my first trip, early in 1977, I had an after-dinner conversation with Dick and Peter Ordeshook during which Peter explained the two-space theory that he and Mel Hinich had developed.