A planning model of the natural gas pipeline network

3. Whan a map, drawing or chart, etc., was part of the materiel being photographed the photographer followed a definite method in "sectioning" the material. It is customary to begin photoing at tha upper left hand comer of a large sheet and to continue photoing from left to right iii equal sections with a small overlap. If necessary, sectioning is continued again — beginning below the first row and continuing on until complete.