Most hidden surface algorithms require a considerable amount of computation for all but the simplest images. This prevents their use in real time systems where new frames may be calculated at a rate of 25 per second. The paper presents an approach suitable for fixed models, such as those used in flight simulators, where most of the time consuming computation may be performed when the model is first created. The technique is to test for surface proximity in a well defined manner, ‘well spaced’ surfaces requiring a simple measure of distance to determine priority, and ‘closely spaced’ surfaces being modified until they are ‘well spaced’. This modification is only in the representation of the surface and does not affect its final appearance in the picture. The work to be described is part of a project financed by the Science Research Council, to which grateful acknowledgement is made.