Why the 4-point grid system dominates UI design
Briefly

One of the most important rules of modern UI design is to maintain a clear visual hierarchy. To achieve this, spacing units must follow a consistent pattern, typically by scaling the base unit with a fixed proportion.
The 4-point grid hits the sweet spot: it's not too small to go unnoticed, nor is it too large. For example, 2-point increments might feel too fine, while 6-point or 8-point increments can feel like too large a change.
Different devices have varying screen resolutions and pixel densities. A high-density display packs more pixels than a low-density display. To keep UI elements at a consistent physical size, devices scale the interface based on pixel density.
A pixel is the smallest unit on the screen, and all elements must have sizes that are whole numbers. The same applies to the spacing and distance between elements.
Read at Medium
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