What type of angular measurement relates to zenith distance?

Zenith distance is directly associated with the concept of vertical angles in the context of angular measurements. Vertical angles are measured from the horizontal plane up or down to a point in the sky or on the ground. Specifically, when determining the zenith distance, one is measuring the angle from the zenith (the point in the sky directly above the observer) downward to an object or celestial body.

In astronomical observations, zenith distance helps in calculating the altitude of celestial objects. The closer the object is to the zenith, the smaller the zenith distance. Understanding this relationship is crucial for various geodetic and astronomical applications, as it plays a significant role in triangulating positions and measuring heights.

The other types of angles listed do not directly correlate with the concept of zenith distance. Horizontal angles deal with measurements parallel to the ground surface, inclined angles involve surveying techniques related to sloped surfaces, and circular angles apply to angles in a circular plane which do not specifically pertain to the vertical positioning of objects.