An analogy is shown to exist between free convection in a rotating porous layer subject to both gravity and centrifugal forces, and natural convection in an inclined porous layer subject only to gravity. An analytical three-dimensional solution to the convection problem in a vertical porous layer located far away from the center of rotation and subject to gravitational and centrifugal forces is presented. Resolving the gravity related Rayleigh number for the inclined porous layer into horizontal and vertical components and considering the rotating porous layer in a vertical orientation, the analogy between the two cases is derived. A transition point beyond which no real solutions exist for the critical value of the centrifugal Rayleigh number was evaluated. This transition is shown to be similar to the transition found for the angle of inclination in the inclined porous layer. The marginal stability criterion is established in terms of the critical centrifugal Rayleigh number and a critical wave number. The linear stability theory is used to establish the conditions necessary for different types of convection patterns to exist, whilst a three-dimensional spectral method is used to predict theoretically the convective flow structure.