Two-dimensional cut through the stellar sphere, at the position of the spotcenter in the direction perpendicular to the line of sight. The green dashed line represents the spot feature as it would be seen in three dimensions on the stellar sphere. The size of the spot is determined by the angle α (blue). The minor arc d (red) between the spotcenter and any pixel location on the spot can be found through the angle Δσ (red) times the stellar radius in pixels r_s. Values of Δσ are derived from Eq. (2). Every point on the stellar sphere, corresponding to the spot feature, needs to fulfil the condition: Δσ ≤ α.