[seri4l]

The distortion is not because the Earth is 3D and maps are 2D, it's because the surface of the Earth isn't Euclidean like a plane is.

That means the meridians (the vertical lines you see on a map) which are perpendicular to the parallels (the horizontal lines on the map) intersect themselves at the poles (!). You can easily see how this leads to distortion of the areas closer to the poles (like Europe) on any projection where the meridians are parallel. Projections like Mercator account for this distortion by making the distances between the parallels bigger as one moves towards the poles. That's what makes Europe and Greenland huge, but more importantly makes it possible that any arbitrary straight line on a Mercator map corresponds to a straight line on the globe, which was huge for navigation.