Each vowel claims the region of acoustic space closer to it than to any rival — its territory. Put seven vowels together and the space tiles into a mosaic. Drag one and notice: only the neighbouring territories redraw; the distant ones don't even register it.
Strip the territories away and keep only who borders whom: here is the network of contrasts that holds the inventory together. Move a vowel up above, and the links rewire only in its neighbourhood — while the global dispersion, how much the system fills the space, barely stirs.