All-inorganic cesium lead halide perovskite nanocrystals (IP-NCs) are nowadays extensively studied because of their outstanding optoelectronic properties. Being of a cubic shape and typically featuring relatively narrow size distribution, CsPbX3 (X = Cl, Br, I) nanocrystals are the ideal starting material for the development of homogeneous thin films as required for photovoltaic and optoelectronic applications. Recent experiments reveal the spontaneous merging of drop-casted CsPbBr3 nanocrystals, which is promoted by room humidity and can be accelerated by mild temperature treatments. This fusion can be arrested by electron beam irradiation, which induces new C=C bonds between the surface ligands making the IP-NCs more stable. Here, we make use of atom-resolved annular dark-field imaging microscopy and valence electron energy loss spectroscopy in a state-of-the-art low-voltage monochromatic scanning transmission electron microscope, to investigate the aggregation between individual nanocrystals at the atomic level. We show that the merging process preserves the elemental composition and electronic structure of CsPbBr3, and takes place between nanocrystals of different size and orientation. In particular, we reveal seamless stitching for aligned nanocrystals, similar as reported in the past for graphene flakes. Since the crystallographic alignment occurs naturally in drop-casted layers of CsPbX3 nanocrystals, our findings constitute the essential first step towards the development of large-area nanosheets with bandgap energies predesigned by the nanocrystal choice.