Tectonic plates are curved -- they can cover very large areas of the planet (consider the pacific plate), yet are only a few tens of kilometers thick.

The plates are curved to fit the shape of the Earth. The Pacific Plate, which spans roughly a quarter of the Earth's surface area, would stick thousands of kilometers into space were it flat.

The tectonic plates are curved to fit the surface of the earth. However, it might be more correct to say that the surface of the earth is curved because the plates are curved.

Since the plates make up the outer crust of the planet, their shape determines the shape of the planet. Because the earth's gravity is quite strong in all directions, the whole planet, including the plates on the surface, is held in a curved, spherical shape.

Yes, they are actually spherical caps that follow the curvature of the earth. In fact, they DEFINE the curvature of the earth. They are called plates because we usually depict them on a 2D map surface... a flat plane... but really the earth is round!!!

Tectonic plates are curved to fit the surface of the earth. For instance, the Pacific Plate (on which we live!) curves across about 40% of the earth near the equator. If tectonic plates were truly flat, they would have to be very small and there would be thousands of them to fit around the spherical shape of the earth - rather like all the little flat mirror pieces that are glued onto a ball to make a discoball. Instead, the earth has about 10 major tectonic plates that can be thousands of miles across each.