The characterization of samples is critical to all X-ray absorption spectroscopy (XAS) measurements, whether seeking calibrated data for comparison with advanced theory or relative data for fingerprinting analysis via methods such as principal component analysis or linear combination fitting. For solids, the thickness, thickness profile and integrated column density are relevant. More subtle but similar is where the beam intersects a variable projected thickness of the sample. In this chapter, this variation of the projected thickness is defined and the name the projected roughness is suggested. This projected roughness causes changes to the structure of the near-edge XAS and pre-edge and X-ray absorption near-edge structure (XANES) in particular. Included in this concept is local heterogeneity, which includes the variation of local composition across a sample, whether thickness, mass density or nanostructure. The impact of projected roughness scales with the mass attenuation coefficient and so will be most pronounced at low photon energies or high atomic number, where tabulations show the greatest divergence. It is demonstrated that projected roughness can easily affect the X-ray absorption fine-structure oscillations by 2% or more, especially in an energy-dependent functional in the XANES region. It therefore affects the applicability of advanced theory to predict XAS spectra. Projected roughness can compromise the fingerprinting of a reference material or unknown in pre-edge structure and can affect the first part of XANES for matching to unknowns or for principal component analysis and related approaches. The impact of projected roughness can be used to characterize the effect and it can be corrected to improve measurement accuracy, theoretical structure identification and intercomparability.