Where rates are shown on the maps, it should be thoroughly understood that they are given to indicate the general line of rates applying, and that there may often be changes in individual rates that are not shown on the map. Those familiar with the use Of rates will thoroughly appreciate the impossibility of changing these maps in every case where individual rates are changed. The grouping of territories for freight rates is subject to frequent minor changes and occasional material ones. For this reason it is impossible to show the exact current grouping of freight territories in a set of traffic maps. However, these maps were drawn with care and with as much accuracy as possible from traffic publications, and the general grouping does not often change materially. Moreover, every effort is made to correct the plates for material changes. For this reason the maps form a basis for the study of freight rate adjustment throughout the country. In order that a student may obtain vivid mental pictures that will aid him in understanding the rate structure, the colored maps are a necessity.