Fortran projects are famous for their large modules. Actually, we may also find very large files in legacy projects written in other languages, like Java, PHP, etc. These projects sometimes have files with thousands of lines of code. Fortran projects suffer more from large files I’d say, because:

• IDE support is not great. It’s often still hard to navigate to definitions or usages. There isn’t any support for automated refactorings, like extract function, move function, add parameter, etc. You often can’t get a clear overview of the structure/outline of a file.
• There are no strict indentation rules, making it easy to create a complete mess. Not everyone uses code formatting tools. Code formatting tools that exist and are used, aren’t always very good or easily configurable.
• Fortran code can be hard to read, partially because a lack of curly braces. It’s hard to visually recognize blocks of code. Another reason is that commonly there’s no distinction in letter casing between type names, function names, variable names, etc. Other languages may use CamelCase for types, CAPS for constants, pascalCase for methods, snake_case for functions, etc. In Fortran code, it’s all snake_case.

If there’s anything we can do to make Fortran code easier to deal with, it’s to split the code into smaller parts. We need to have many more modules, each with distinct topics and concerns, so we can get a quick overview of the application’s domain and capabilities. Additionally, this will help us find the right place when we want to make changes to the code.