One possible solution to the problem of space and time in our cities is the megastructure. Essentially a city in one vast, continuous building, the megastructure would encompass dwellings, stores, service facilities, offices and recreation centers within one concentrated urban structure. Everything would be within walking or easy driving distance, including the count @ side, which would surround the city, not be broken into fragments within it. This concentration would provide a richer, more diverse life than that of suburbia, while preserving the countryside from suburban sprawl. In addition, it would reduce the size of today's metropolis to the more workable, cohesive political unit of under 50,000 population that environmental planners suggest. The plan for one such magastructure is shown here, a "contour-rise" urban core designed for the Santa Monica mountains of southern California by Cesar Pelli and A. J. Lumsden, Director of Design, Daniel, Mann, johnson and Mendenhall.