Does the layer in the architecture have a system of levels or a layered structure?

A layer in architecture usually does not possess a system of levels or a layered structure by itself. A layer is a logical level of abstraction that groups components with similar functions (for example, presentation layer, business logic layer, data access layer).

A layered structure (or multi-tier architecture) is formed from several such layers stacked on top of each other, where each layer interacts with its neighboring layers.

Thus, a layer is an element of the layered structure, but by itself, it does not contain levels within. It represents a single level in the architecture's level system.