1. A method of making a synthesis color photographic map, on a first predetermined scale and covering a wide geographic area, from a number of forestry base maps, each forestry base map covering a selective portion of said wide geographic area on a second predetermined scale larger than said first predetermined scale, said method comprising the steps of: coloring each of said forestry base maps according to a given identification color code: color photographying said forestry base maps thus colored while reducing the scale thereof to said first predetermined scale to thereby obtain color photographic base maps having said first predetermined scale, and assembling said color photographic base maps together to form said synthesis color photographic map.