A skills matrix makes a skills mapping easy to grasp. The rows are typically employees or roles. The columns are the skills that matter for the job. Each cell holds a level, for example from 1 to 4.
The matrix is used for three things. It shows gaps, where no one knows enough. It shows vulnerabilities, where only one person can handle an important task. And it provides a shared language for the conversation about development.
Keep the matrix simple. A few clear skills are more useful than a long list no one updates.