Axis is an imaginary line used to organize a group of elements in a design, about which forms and spaces can be arranged in a balanced or symmetrical manner. The axis provides length and direction, induces movement, and promotes views along its path, as well as uphold a feeling of order. Although the axis is invisible to the eye, it can be made more apparent by defining the edges of surrounding elements. It is commonly conceptualized in architecture with defined endpoints but can be continuous in virtual spaces with infinite scroll. It is represented by a dashed line in diagrams and drawings.
Source: Architecture: Form, Space, and Order by Francis D. K. Ching; GharPedia, “Ordering Architecture Principles of Design”
Example from original source:
Example from different source:
Source: Melissa Mandelbaum, “Design Principles”
Real life example:
