The Vertex is a mathematical intersection of the prime vertical and the ecliptic, often referred to as the "Third Angle" of a chart. It functions as a point of "fated" encounters. It is often activated when you meet people who significantly change the course of your life or when external events beyond your control occur.
The astronomy in these guides is computed, not copied: sign boundaries, aspect angles and planetary positions are calculated on StarBind's own servers from the same JPL planetary data NASA uses, accurate to fractions of an arcsecond.