Under some conditions, different map units are used for the X and Y dimensions.
Consider a contour map of soil temperature as a function of depth and time. Depth is measured in feet, while time is measured in days. Clearly, one day is not equivalent to one foot. The two axes must be scaled differently because two different types of units are used for the two axes. Depth data might be collected every half foot from zero to four feet in depth, and the time data might be collected every day over a 30-day period. The depth axis extends four units and the time axis extends 30 units. Default scaling would produce a map six inches long in the time dimension by 0.8 inches high in the depth dimension. To create a square map, you must clear the Proportional XY scaling box on the Scale page and then set the map scaling so 30 units in the time dimension is equal to four units in the depth dimension. The map is then plotted at six inches by six inches.