Button design for map overlays: 2

A new approach to button design has recently been proposed that uses natural segments, instead of even intervals, on the weight value range in determining the number of tabs that should be incorporated in a button system and the value each button carries. Button systems so designed do not have the problems of redundancy and underrepresentation that are common to the conventionally designed button systems. Presently limited to the map overlays that involve only two parent maps, this approach is extended to the case of three parent maps in this paper.