Most well-known litho-simulation packages work with Manhattan unit cells to exploit the advantages of fast Fourier transforms. Simple 1D features with arbitrary orientations may lead to the fact that quite a large 2D area is needed to describe those features. The obvious consequences are that the feature is approximated by a staircase and that the pitches are related to the angle of rotation. The latter leads often to an increase in computation time, especially when the topography of the mask is taken into account. An obvious way of avoiding that is to rotate the features and all pupil functions or lens properties to x- or y-axes. However, for anamorphic systems, where the demagnifications are fixed in absolute space, this is not straightforward and several actions have to be taken. We described how to do this exactly. It will be shown that the aerial images from a full 2D simulation compare well with that of an equivalent 1D version.