100 people working for the architectural model makers Raymond Lester Associates in the three years before the opening of the 1964 World's Fair. The model was constructed in 273 sections, depicting a total of 895,000 individual structures; the section showing the Far Rockaway neighborhood was never installed, due to space limitations. The Panorama was one of the most successful attractions at the 1964 Fair, with "millions" of people paying 10 cents each for a 9-minute simulated helicopter ride around the city. After the Fair closed, the Panorama remained open to the public, and Lester's team updated the map in 1967, 1968, and 1969. After 1970, very few changes were made until 1992, when again Lester Associates was hired to update the model to coincide with the re-opening of the museum, after a two-year total renovation of the building by Rafael Viñoly. The model makers changed over 60,000 structures to bring it up-to-date at that time. In March 2009, the museum announced the intention to update the Panorama on an ongoing basis. To raise funds and draw public attention, the museum will allow individuals and developers to have accurate scale models made of buildings newer than the 1992 update created and added, in exchange for a donation of at least $50. More-detailed models of smaller apartment buildings and private homes, now represented by generic models, can also be added. , the original twin towers of the World Trade Center are still on the map, even though some new buildings have been built on the actual site; the museum has chosen to allow the destroyed structures to remain until construction is complete, rather than representing the ongoing construction. The first new building to be added under the new program was the new Citi Field stadium of the New York Mets; the model of the old Shea Stadium was to be displayed elsewhere in the museum. The mechanical "helicopter" vehicles for conveying exhibition visitors were showing signs of wear, and were removed before the 1994 reopening. The current installation by Viñoly features accessible ramps and an elevated walkway which surround the Panorama, allowing viewers to proceed at their own pace, or to linger for as long a look as they desire. Because of space constraints, portions of the walkway are cantilevered over the outer edges of the map, but a glass floor still allows views of the model below. As in the original