The concept of modularity and layered architecture are closely related in software development, both playing key roles in creating structured and manageable systems. Here’s how they connect:

1. Modularity refers to dividing a program or system into separate parts that can be developed, tested, used, and understood independently. Each module encompasses everything necessary to perform its specific function and typically has a clearly defined interface for interacting with other parts of the system. Modularity allows developers to work on different parts of the system simultaneously, simplifies maintenance and upgrading of the product.

2. Layered architecture is a way of organizing a system where components are separated into layers with clearly defined roles. Each layer performs specific functions and provides services to the next level. For example, a typical three-tier architecture includes a presentation layer (user interface), business logic, and data access layer. This architecture not only makes the system easier to understand and develop but also helps to isolate changes in one layer from affecting others.

The connection between modularity and layered architecture involves:

- Both concepts promote separation of concerns within the system. Modularity divides the system into functional blocks, while layered architecture organizes these blocks into a hierarchy of layers with dependencies only pointing "upwards."

- In a layered architecture, each layer can be seen as a collection of modules, which simplifies the replacement or updating of individual layers without impacting others.

- Using both concepts allows for a more flexible approach to scaling and maintaining the system, as well as facilitates integration with other systems and technologies.

Together, modularity and layered architecture provide a robust foundation for developing resilient and scalable software systems that can adapt to changing requirements and technologies.