The notion of Earth's surface being divided into seven gigantic flat plates is referring to the theory of plate tectonics. According to this scientific model, the Earth's lithosphere (the rigid outer layer) is divided into several large plates that float and move on the semi-fluid asthenosphere beneath. These plates interact at their boundaries, leading to various geological phenomena such as earthquakes, volcanic activity, and the formation of mountain ranges.
While it is true that the Earth is approximately spherical in shape, the plates in plate tectonics theory are not meant to represent perfectly flat objects adhering to the Earth's surface like sticking plates onto a globe. Instead, they represent large sections of the lithosphere that move and interact with each other. Think of the plates as rigid pieces that fit together, similar to jigsaw puzzle pieces.
On a model globe, it is not possible to accurately represent the complex three-dimensional nature of plate tectonics. The scale and size of the Earth, as well as the intricate interactions between the plates, cannot be fully captured by a small-scale model. The representation of the plates as flat divisions is a simplification to help illustrate the concept of how different sections of the Earth's crust move relative to each other.
In reality, the Earth's lithospheric plates have irregular shapes, and their boundaries can be intricate and complex. They are not flat, uniform, or restricted to a fixed number. The seven major plates commonly referred to are the African Plate, Antarctic Plate, Eurasian Plate, North American Plate, South American Plate, Australian Plate, and Pacific Plate. However, there are also numerous smaller plates and microplates that contribute to Earth's tectonic activity.
So, while it may seem counterintuitive to depict flat plates on a spherical object, the representation is simply a visual aid to help us understand the dynamics and movements of Earth's lithosphere.