The way it works is, there are 16 figures, each of which has its own pattern of dots, its own meaning, its own name, and a correlation with one of the seven planets of antiquity. You can see the figures
here.
Each figure is composed of four rows. Each row contains either one or two dots. And this is where Cortez's four-card spread comes in. In her spread, which is laid out vertically, each card can be matched to one row of a geomantic figure. Her method is to derive the geomantic figure from the four-card spread by a simple binary analysis of the cards. If the card number is odd, the geomantic row receives one dot. If the card number is even, the geomantic row receives two dots. Thus, a geomantic figure (called a Witness) is derived from the four-card spread. This geomantic figure, since it has its own meaning and astrological correlation, can be interpreted so as to provide an overall direction for the spread.
Then, a second geomantic figure (another Witness) can be derived, this time by analyzing the cards by color rather than by number. The differences between the two Witnesses can be seen as either providing a temporal framework (first this, then that), or a psychological framework (inner mind, outer personality).
Finally, the two Witnesses together can be used to generate a third geomantic figure, called the Judge, by adding together each row of the two figures. The Judge provides an ultimate outcome, and Cortez has a list of six rules governing the analysis of the three figures together (i.e., what if you have two negative Witnesses and a positive Judge, etc.).