Geomancy sensu stricto is a technique of divination which makes predictions about the future from figures derived from a randomly generated pattern of dots. Geomancy means "earth prophecy" or "earth divination" in Greek; this is because these dot patterns were traditionally marks in the ground or in a sand tray. The dot patterns in my geomancy pages are marks on paper or in my computer's memory, so this name might not seem to apply. However, interpreting "earth" to mean "solid matter", geomancy is about interpreting persistent patterns (as opposed to the transitory patterns interpreted in pyromancy, aeromancy, and hydromancy), so it's particularly amenable to rational consideration and mathematical analysis.
Geomantic figures are stick figure-like patterns composed of a stack of four evenly spaced rows of dots, each row containing either one or two dots; the first central moment of the dots in each row lies on the same line. Each row has either one or two dots, and there are four rows, so there are 2^4 = 16 geomantic figures. These figures have Latin names and (surprisingly, given the unintuitive names assigned to another major set of natural dot patterns, constellations) bear a striking resemblance to their namesakes.
Below is a chart I made of all sixteen geomantic figures; the dot patterns are overlaid with sketches showing my interpretation of each figure. Each row of a figure corresponds naturally to a binary digit (that row's number of dots mod 2: 0 for two dots, 1 for one dot), so each figure corresponds to a nibble of binary digits, which I have converted to a decimal number and written below each figure. The most significant digit of the nibble corresponds to the figure's head (top row), the second most significant digit corresponds to the figure's neck (second-from-top row), etc. Each figure is beside its inverse, the figure made by swapping all one-dot rows for two-dot rows and all two-dot rows for one-dot rows, or, equivalently, the figure which corresponds to the decimal digit that, added to the figure's original corresponding decimal digit, gives 15, or a nibble of 1111. ("Inverse" unfortunately doesn't mean additive inverse here: 15 is not 0 mod 16.) I have marked with an asterisk figures that can become Judges.
Hopefully my sketch interpretations of these figures are clear. Laetitia is a rainbow. Rubeus is an overturned goblet (spilling red wine). Fortuna Minor and Fortuna Minor show sunbeams signifying fortune coming from the heavens and from Earth, respectively: it's less auspicious to rely on outside help, I guess. Amissio is an overturned, empty cup; Acquisitio is a cup piled up with wealth. Conjunctio is a crossroads. Carcer is a chain link. Tristitia is a broken arch.
Each figure has at least one paired figure. I have connected pairs with a double-headed arrow. For example, Amissio (loss) is paired with Acquisitio (gain). Eight figures are paired with their inverses. Interestingly, these figures are the eight that can become Judges. There are eight figures with non-inverse pairs: Rubeus (the emptied goblet) is paired with Albus (the filled goblet); Puella (the girl) is paired with Puer (the boy); Cauda Draconis (the tail of the dragon) is paired with Caput Draconis (the head of the dragon); Tristitia (sadness) is paired with Laetitita (happiness). These figures are mirror images of their pairs; the mirror plane cuts between the neck and the body of the figure, equidistant from and parallel to the second and the third rows. The purported divinatory significance of each geomantic figure is discussed in detail in Agrippa's "Of Geomancy".