  When pressurized, the heavy fermion compound CeNiC$_2$ reveals a rich
electronic phase diagram and shows unconventional superconductivity with a
transition temperature $T_c$ $\sim$ 3.7 K, the highest among Ce-based heavy
fermion superconductors [S. Katano et al., Phys. Rev. B. 99, 100501(R) (2019)].
Understanding of this appearance of superconductivity in the vicinity of
magnetic quantum critical point is still lacking. Given that physical
properties of CeNiC$_2$ are sensitive to subtle changes in the interatomic
distances, information on atomic coordinates may offer essential insights into
the local lattice arrangements, thus the mechanisms behind the exotic phases
and phase transitions. However, extraction of precise information on the atomic
coordinates under pressure remains a challenge. To find a correlation between
the local lattice environments and exotic physical properties in CeNiC$_2$, we
investigate its crystal structure from ambient pressure to 18.6 GPa via single
crystal X-ray diffraction. The pressure dependence of lattice parameters
reveals anisotropic linear compressibility, $|\kappa|$, following the
relationship $|\kappa_{a}|$ (3.70$\times$10$^{-3}$ GPa$^{-1}$) $>$
$|\kappa_{c}|$ (1.97$\times$10$^{-3}$ GPa$^{-1}$) $>$ $|\kappa_{b}|$
(1.39$\times$10$^{-3}$ GPa$^{-1}$), and a large bulk modulus, B$_0$ $\sim$ 134
GPa. Although the atomic coordinates between Ce and Ni remain unchanged under
applied pressure, direction of the first nearest and the second nearest
neighbors between both the Ce-Ce and Ni-Ni atoms switch $\sim$ 7 GPa. Notably,
this is the same pressure that antiferromagnetic ordering temperature reaches
maximum in the pressure temperature phase diagram of CeNiC$_2$. Our results
suggest that the direction of nearest neighbors interchange might play a key
role in the suppression of magnetic order and the enhancement of Kondo effect.
