Schematic illustrating examples of additive and multiplicative systematics on the galaxy density field. Yellow stars and blue ellipses represent stars and galaxies, respectively. The left panel shows the true galaxy and star locations, while the right panel represents the measured locations. The regions where the measured and true galaxy distributions differ are circled on both panels, with the colour of the circle indicating the type of systematic that is generated. An example of a multiplicative systematic is the unrecognized blending of two or more distinct galaxies in the observed distribution, resulting in a multiplicative effect to the observed number density. An example of an additive systematic is when stars are misidentified as galaxies in the measured distribution. This illustration shows how multiplicative systematics depend on the galaxy density field while additive ones are independent of the galaxy distribution.