Can you explain what the C4 model is and how it is used for visualizing system architecture?

The C4 model is a method for visualizing software architecture, developed by Simon Brown. It consists of four levels of diagrams that help systematically reveal the structure of a system from an overall overview to detailed components:

1. Context — shows the system in its environment, interactions with users and external systems.
2. Containers — breaks down the system into high-level parts (applications, services, databases), showing their interactions.
3. Components — details the containers into individual components with their responsibilities.
4. Code — the most detailed level, showing the internal structure of components (classes, modules).

It is used for a clear hierarchical description of architecture, facilitating communication among developers, architects, and other stakeholders. In Go projects, for example, at the container level, you can show services and databases, and at the component level, packages and modules.