This is a map of the organs and the areas reflecting their condition. As you can see, its yet another example of a system in which "The exterior reflects the interior." There several maps of foot diagnosis with significant differences in locations. Modern Reflexology is a partial derivative of these systems.
Its interesting to note that several of them share a location with an acupuncture point. The kidney area is also the acupoint KD 1 which is perhaps the point which has the strongest effect on the kidneys' functions of any point on the Kidney meridian.