The authors wish to thank The Alcoa Technical Research Center for supplying the specimens and performing the compression tests. This work was supported by the MRSEC program of the National Science Foundation under DMR-0079996 as well as Lawrence Livermore Laboratory DOE/DoD Joint Program. An behavior of grain boundaries of the polycrystalline materials over a wide range of length scales during plastic deformation is considered. Electron backscattering diffraction and orientation imaging microscopy provide automated scanning measurements of the lattice orientation near grain boundaries. These methods are useful to set the necessary length scales. The data are presented for directionally-solidified pure Al with a strong <001> column texture, subjected to uniaxial compression tests. It is shown that the data obtained for estimation of geometrically-necessary dislocations (ones that are required to support a particular curvature in the crystallographic lattice at any given point of deformed structure) are reliable.