Like Arcanist Lupus said, it depends on whether you mean simulating elevation on your board, or as a mechanic. Here are some brief notes for either case, but I will improve the answer when you clarify your question a bit.
As far as simulating elevation visually is concerned, this can be done with a contour elevation map. These are maps which have bands at each gradation of elevation. Every point along a single band is exactly the same elevation, and the distance between any two bands covers the same amount of elevation. If two bands are close to each other at a point, that indicates a steep elevation, whereas a further distance is representative of a more gradual slope.
As far as mechanics are concerned, elevation can impact movement and combat. Some parts of your contour map could have bands which are very close together, to the point where they are too steep to be passable. Additionally, you can have a movement penalty for increasing in elevation, or a movement boost for decreasing in elevation. You could also add a chance for a vehicle to slide down the hill they are on if they are ascending too rapidly. A vehicle at a higher elevation will have a longer range than one at lower elevation. You could implement range in your combat with physical measurements (like inches or mm), and increase or decrease that range in game based on the relative elevations of your vehicle and its target. So if you were to attack up an elevation, you would have reduced range, but attacking down elevation will increase range.