Very large fields of view are needed in certain training scenarios (i.e. flight training, etc.). One solution is to provide a display screen in the shape of a sphere, surrounding the student (or observer) station. The image quality and other display parameters of such a system are dependent upon the geometry of projector(s), screen and viewer(s), as well as the image generation and projection technology. Another major factor is the shape of the screen (usually spherical) and the extent of "closure" of the dome. This last factor is sometimes overlooked in the design and so performance suffers. This paper discusses the display parameters of dome systems and presents performance of such systems as a function of screen size, shape, and quality, the generation and projection of the visual scene, and the overall system geometries.