An investigation is made on the applicability of method of representing by Cartesian grid to calculate flow over natural terrain. Model hill geometry with different maximum slope angles is chosen and calculations by both Cartesian and Boundary-fitted coordinate representations are made. Computations are performed for laminar flow at different Reynolds numbers and turbulent flow conditions. Results in terms of mean velocity distribution, streamline, vorticity distribution and velocity vector close to the surface are analyzed and discussed. The study indicates that to calculate flow over undulating natural terrain, rectangular coordinate method of representing the geometry is able to capture most of the flow phenomena and it can be a viable alternative.