Videotex, the narrowband home information retrieval service, requires that information pages be composed of a set of predefined primitives; in particular, alpha-geometric videotex services are based on geometric primitives. This paper discusses picture description primitives suitable for picture synthesis and picture approximation in alpha-geometric videotex data bases. Simulations of these activities are used to evaluate the suitability of several previous and new proposals. Suitability measures are based on the ease of encoding and the compactness of the descriptions. The primitive set consisting of straight lines and cubic splines is shown to be an attractive choice.