The spread footing behaves like an inverted cantilever with loads applied in the upward direction. As a rule, a spread footing is a quite rigid element therefore, the applied soil stresses are almost linear and in case of a symmetric (with respect to the pedestal) footing, they are orthogonal. These soil pressures are the loads carried by the footing that behaves like a slab and is deformed by the way shown at the figure.
The real deformation is in the order of a millimeter and although it is not visible to the human eye, it always has that same form. The reinforcement is placed at the lower surface of the footing both along the x and y axis.