In the limit at which geometric optics is valid, a light signal may be represented (in special relativity) by a (straight) null line. If we consider an eventP, then the past null cone drawn fromPrepresents all events visible to any observer atP. The configuration of events perceived by any one observer may be obtained by projecting this cone onto the 3-flat orthogonal to the observer's 4-velocity in a suitable fashion. In this paper a projection technique is described and leads naturally to a system of spherical coordinates for each observer. The transformation of coordinates for two observers is obtained and some applications are discussed.