Pixel pitch and where the nearest viewer stands in — a verdict, the three distances that matter, and a top-down picture of the bands out. Then the reverse: which pitch a given distance needs, with links to the real panels in that class.
Pitch classes comfortable from here: 0.9 mm, 1.2 mm, 1.5 mm, 1.9 mm.
Cameras are less forgiving than eyes: broadcast and IMAG walls are commonly specified finer than the distance rule alone suggests, to manage moiré and close-ups. The rules above are conventions — content, brightness and how the audience is spread all move them.
The industry rule of thumb is one metre per millimetre of pixel pitch: a 2.6 mm wall from about 2.6 m, a 3.9 mm wall from about 4 m. At that distance the pixels blend into a picture on typical content. Crews plan for two to three times that for comfortable viewing.
A person with 20/20 vision resolves about one arcminute, so individual pixels disappear at roughly 3.4 m per millimetre of pitch — about 9 m for 2.6 mm, 13 m for 3.9 mm. That is the physics limit; the 1 m per mm rule is looser because real content hides the grid well before then.
By the 1 m per mm rule anything up to 5 mm works; by the comfortable 2× rule, 2.5 mm or finer. On camera, go finer still — broadcast walls are specified tighter than the eye needs to manage moiré and close-ups.
Also: pixels & size, power & circuits, weight & points — or the planner for the whole job.