Velodromes can range from less than 200 metres (with very steep banking) to over 450 metres on outdoor, concrete tracks. However, Olympic standard velodromes need to be 250 metres in length, completely covered, and are made of wood.
Wooden velodromes need to be hard, straight and hold their shapes as they age. For this reason, most are built from Baltic Pine which often comes from the same plantation in Finland that has supplied virtually every recently built velodrome. I am told a 250 metre track has 60km of 40mm x 40mm x 6m planks and is held together by 360,000 nails.
Track surfaces last for decades, and get better as they get older: This is because the wood hardens and the track therefore gets faster.
The area infield of the track accommodates team support staff such as coaches, managers, mechanics, and masseurs; the press; officials and timing and in the case of the track at Atlanta, the event office space. Offices are usually underground, but the Atlanta track was temporary so no underground facilities were dug. The Atlanta track was sold after the 1996 Games and is now part of Los Angeles Disneyland.