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 General Electric Review

Fig. 193. Location of Water-Power Developments of 1,000 Horse Power, and Over, and Power Sections of Streams in the United States

The original of this map would have pins in two different colors. The photograph taken from the map would be retouched by the use of a pen so that squares would replace dots for one of the two colors of pins. The illustration shows a contrast of dots of two shapes rather than dots of two colors