Otherwise, the course is on closed roads for the 1st 3.5 miles, then on a well compacted gravel path for a short distance before hitting tarmac again by 4 miles. There is a pinch point at 3.1miles between immovable bollards. Apart from a section of well compacted path from Mile 13 to 14.5 (and 22 to 23.5 on the 2nd loop), the race is on road or pavement. And you finish with nearly a lap of the track.
Apart from running around a track for 26.2miles, i doubt there are many flatter marathons. There is a slight sting at 24.1miles where you go through an underpass and so have to climb the slope on the way out!
There is a route and elevation profile on the website now under the "About" tab. My elevation profile from 2011 is below. Obviously this was on the old course but it won't be significantly different. It may look a bit mountainous but the altitude range is only from 51 to 72m