20250327 16074000 1.0 TRUE Index250k The National Topographic Series was a federal government inititive to create maps for the whole country, at a variety of scales. This particular layer contains the index of the 1:250 000 maps. Each of these maps covers two degrees of longitude and a single degree of latitude. The naming convention works as follows. At the 1:1 000 000 level, each sheet has a number. - Each of these numbered 1:1M sheets is further divided into 16 lettered 1:250k sheets. - these are labeled A-P, commencing with the letter A in the bottom right, and proceeding in a zig-zag as you move northward. Thus the final layout is: M N O P L K J I E F G H D C B A - Each of these lettered sheets is further subdivided into 16 numbered 1:50k sheets. Each of these maps covers half a degree of longitude and a quarter degree of latitude. - this numbering system follows the pattern as above, with the origin in the bottom right, zig-zagging as you move northward.