Paul wants to decide for whom he will vote in an upcoming municipal election. Paul is primarily concerned with one attribute of the candidates: how liberal or conservative they are. He makes a plot with “very liberal” on one end and “very conservative” on the other end. He plots both candidates along this line, and then draws a dot indicating where his ideal candidate would fall on the line. Paul then decides for whom to vote based the closeness of each candidate to his ideal point along this line plot. This process is a simple use of which concept from class?