Fibers can be arranged in what are called one-dimensional (1D) and two dimensional (2D) arrays.
A 1D array is a single line of fibers, and a 2D array is a grid of fibers in both X and Y dimensions. In both cases, they are specified by the spacing between fibers. In the case of 1D array, there is a single defining dimension denoting the center-to-center position of the cores of the fibers.
For 2D arrays, there are two dimensions, X and Y, that define the core positions. One-dimensional arrays can be manufactured by several different techniques. The manufacturing technique will define the position accuracy of the fiber cores.