  Terrace-sized, single-orientation graphene can be grown on top of a carbon
buffer layer on silicon carbide by thermal decomposition. Despite its
homogeneous appearance, a surprisingly large variation in electron transport
properties is observed.
  Here, we employ Aberration-Corrected Low-Energy Electron Microscopy (AC-LEEM)
to study a possible cause of this variability. We characterize the morphology
of stacking domains between the graphene and the buffer layer of high-quality
samples. Similar to the case of twisted bilayer graphene, the lattice mismatch
between the graphene layer and the buffer layer at the growth temperature
causes a moir\'e pattern with domain boundaries between AB and BA stackings.
  We analyze this moir\'e pattern to characterize the relative strain and to
count the number of edge dislocations. Furthermore, we show that epitaxial
graphene on silicon carbide is close to a phase transition, causing intrinsic
disorder in the form of co-existence of anisotropic stripe domains and
isotropic trigonal domains. Using adaptive geometric phase analysis, we
determine the precise relative strain variation caused by these domains. We
observe that the step edges of the SiC substrate influence the orientation of
the domains and we discuss which aspects of the growth process influence these
effects by comparing samples from different sources.
