Most of us are familiar with camber, where the inside of a corner is higher or lower than the outside, creating a banked effect. Gravity can work in your favour - positive camber, with the outside of the track higher than the inside - or against you - negative camber, with the outside of the track lower than the inside.
If a portion of the track has more positive camber than another, it may be worth the sacrifice of a non-ideal line to take advantage of that camber and save time overall. Here we will deal with slope, which refers to a change in altitude parallel to the riding line. Just as turning on the more cambered portion of the track lets gravity work in your favour, braking on a more uphill part of the track or accelerating on a more downhill part may be faster and quicker overall.
Note that slope and camber are intertwined somewhat; when you arc into a banked turn from the outside to the inside of the track, you are turning the positive camber of the turn into negative (downhill) slope. A good rule of thumb is to try and do more of your turning on the more uphill part of the track, as this turns the slope into positive camber, working in your favour.
Another aspect to consider is how the track dips or crests, as this can greatly affect traction. When you ride over the crest of a hill, your bike can unload a significant amount of weight and lose traction; likewise, at the bottom of a dip in the pavement, weight and traction are added. This will benefit braking, accelerating and turning, and going out of your way to take advantage of a dip in the track - or avoid a crest - can save time.
Motocross riders seem to be able to find the optimum lines and manage the tradeoffs almost naturally, but for some reason it is less intuitive on paved tracks. Riders are often more focused on taking the "ideal" line or the line that everyone else uses, and don't consider potential benefits that something different may offer due to changes in the elevation.
Both the AiM EVO4 data acquisition system and the AiM Solo GPS lap timer that I used with Jodi Christie this year record altitude and slope data, and this can be very useful when combined with sector times and the GPS trace to find the optimum riding line. It may seem like a lot of work for little payoff, but consider this: Autodrome St-Eustache is considered a flat circuit, with just seven metres of elevation change. But even here we were able to use slope and altitude data to find a non-ideal and non-intuitive line for Jodi on his superbike that saved as much as a couple of tenths of a second in just one corner.