I have always wondered if it is possible to install pavers on a slope which varies, in other words a non-linear and non-consistent progression from one end to the other as you change grade? I have not encountered this yet, but it seems like it would be a common thing to deal with. I am thinking of an example where a sidewalk is needed to get from the driveway to the front door of a home, over a lawn that has a few gentle rolling hills along the way. Also, the homeowner doe not want steps if at all possible. My thoughts are that when there is a concave situation there would be a gap at the bottom of the pavers, which you would not see, but also, the tops might pinch together tighter which could cause problems with interlock and with proper installation of joint sand. In the case where the grade causes a convex situation on the pavement, I would think that the gaps in the joints would be larger, and possible detract from the overall appearance of the paving system being used, depending on the patten and type. What are your thoughts? I wonder what ICPI has to say about this? I haven't looked in that direction yet.