The Horizon System
The Horizon System is sometimes called the individual sphere because it is based on the Zenith and Nadir of the observer.
Any observation point will render the same overall picture, even though it is being established at a different place every time.
fig 5.1.a the Horizon System
The co-ordinates are measured in azimuth and altitudem and are measured in relation to the local South Point. Therefore, the co-ordinates of this system are related to the observation point only.