Unfortunately I had to leave early, but one of the more striking parts of the lecture on Brasilia this evening was a small side note about Costa's submission. While the other entrants submitted plans with a traditional north arrow, Costa's plan favored the symbology of the plan's layout and thus gave the main axis (itself perpendicular to the topography of the hill) preference, resulting in a perfectly upright 'bird' in plan but a north arrow at that sits obliquely on the page.
L'Enfant, by contrast, oriented the entire city of Washington, DC to ensure unity between the orientation of the Mall and the cardinal convention. Surely Washington benefits from a more or less flat site which allows it to be oriented as such, but the non-cardinal orientation of Brasilia hints also at the ability of the modern vocabulary to escape such literal approaches to planning by establishing its own relative system of meaning. It should also be noted that having a main axis which is oblique to the path of the sun ensures dramatic shadows the entire day-- an asset not to be underestimated when combined with the abstract formalism of Niemeyer & co.