While the aforementioned issues do exist, there is also the fact that when scanning by servos (rotational-based scanning) you are effectively scanning in a "dome shape" - because of cartesian to polar coordinate distortion; it's essentially the same distortion you see in a "naive" implementation of the classic simple ray-caster 2.5D engine (like what the original Wolfenstein 3D game for DOS used in the early 1990s).
Because the ray scan happens in effectively a polar (circular) pattern, but the resulting output is on a 2D cartesian screen - you get a "fisheye lens" like distortion effect.
Expand that to scanning both horizontally and vertically - and you would likely get a weird dome-like effect when plotted.
The solution, though, is fairly simple - you basically multiply the distance (when plotted) by the cosine of the angle - this page explains it rather well.