Famous Central London road which leads up to Buckingham Palace from Trafalgar Square. It's long and straight and perfect for hanging lots of flags along, and using for various festivities.
Although closed to traffic on Sundays, The Mall is the preferred route for many a taxi as it is a useful and relatively untrafficked road. It connects Constitution Hill (and therefore Hyde Park Corner) with Trafalgar Square (and therefore the Strand and the nearby [Victoria Embankment]? which is by far the best route for crossing central London). Victoria is also connected via Spur Road and [Buckingham Gate]?.
It's also an excellent cycle route - it's wide and not too busy, and even then there is a cycle path next to the bridleway which runs down most of its length - this path provides a more convenient way around the traffic lights outside Buckingham Palace.