What is the primary use of a stereoplotter?

A stereoplotter is primarily used for creating topographic maps from aerial photographs. This specialized equipment allows surveyors and cartographers to view two overlapping photographs of the same area from slightly different angles. This provides a three-dimensional perspective of the terrain, enabling the user to interpret the elevation changes and contours. By utilizing the stereoscopic effect, the operator can accurately extract elevation data and map features such as hills, valleys, and other landforms. This process is crucial in topographic mapping because it combines both visual interpretation and precise measurements, making the stereoplotter an essential tool in this field of surveying.

The other options, while related to surveying and map-making in some ways, do not capture the primary and most significant function of a stereoplotter. Measuring distances could occur, but it is not the main focus of a stereoplotter's capabilities. Analyzing aerial photos is a broader action that includes assessing imagery for various purposes, not specifically dedicated to topography. Plotting graphs pertains more to statistical data representation rather than the spatial analysis of landforms that the stereoplotter is designed to perform.