E.g. say I have any array of planes, that for texturing-specific purposes, I want to treat as a single 2d object. Like so:
How would I go about mapping this? (In production, the number of independent objects and their location in the world space is arbitrary.)
One simple solution would be to adapt the technique of Texture Atlases to your problem.
Remember that an entire texture is covered by the UV coordinate range of [0,0],[1,1], and you may apply any subset of that range to a texture assignment. For the example provided in the question, each individual quad would cover a 0.25 x 0.25 subset of the original texture.
This of course can be scaled to an n^2 number of objects, where each object covers a subset size of 1/n x 1/n of the original texture. If utilizing the entire texture and/or keeping the subset textures square is not a requirement, then it can be scaled to any number of potential subset images.
