From 1943 to early 1944, Wright produced four different sketches for the initial design. While one of the plans (scheme C) had a hexagonal shape and level floors for the galleries, all the others had circular schemes and used a ramp continuing around the building. He had experimented with the ramp design in 1948 at the V. C. Morris Gift Shop in San Francisco and on the house he completed for his son in 1952, the David and Gladys Wright House in Arizona. Wright's original concept was called an inverted "ziggurat", because it resembled the steep steps on the ziggurats built in ancient Mesopotamia. His design dispensed with the conventional approach to museum layout, in which visitors are led through a series of interconnected rooms and forced to retrace their steps when exiting. Wright's plan was for the museum guests to ride to the top of the building by elevator, to descend at a leisurely pace along the gentle slope of the continuous ramp, and to view the atrium of the building as the last work of art. The open rotunda afforded viewers the unique possibility of seeing several bays of work on different levels simultaneously and even to interact with guests on other levels. At the same time, before settling on the site for the museum at the corner of 89th Street and the Museum Mile section of Fifth Avenue, overlooking Central Park, Wright, Rebay and Guggenheim considered numerous locations in Manhattan, as well as in the Riverdale section of the Bronx, overlooking the Hudson River. Guggenheim felt that the site's proximity to Central Park was important; the park afforded relief from the noise, congestion and concrete of the city. Nature also provided the museum with inspiration. The building embodies Wright's attempts "to render the inherent plasticity of organic forms in architecture". The Guggenheim was to be the only museum designed by Wright. The city location required Wright to design the building in a vertical rather than a horizontal form, far different from his earlier, rural works. The spiral design recalled a nautilus shell, with continuous spaces flowing freely one into another. Even as it embraced nature, Wright's design also expresses his take on modernist architecture's rigid geometry. Wright ascribed a symbolic meaning to the building's shapes. He explained, "these geometric forms suggest certain human ideas, moods, sentiments – as for instance: the circle, infinity; the triangle, structural unity; the spiral, organic progress; the square, integrity." Forms echo one another throughout: oval-shaped columns, for example, reiterate the geometry of the fountain.