Is there a term like "apparent magnitude" but for things outside of astronomy and depicting area instead of brightness?

Solution 1:

visual angle

Visual angle is the angle a viewed object subtends at the eye, usually stated in degrees of arc. It also is called the object's angular size.
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If one looks at a one-centimeter object at a distance of one meter and a two-centimeter object at a distance of two meters, both subtend the same visual angle of about 0.01 rad or 0.57°. Thus they have the same retinal image size. Wiki

The angle formed by two rays of light or two straight lines drawn from the extreme points of a viewed object to the nodal point of the eye. M-W

Obviously you can apply visual angle to any area/measurement, e.g., height, width, diameter etc.