  Nodal line semimetals are characterized by symmetry-protected band crossing
lines and are expected to exhibit nontrivial electronic properties. Connections
of the multiple nodal lines, resulting in nodal nets, chains, or links, are
envisioned to produce even more exotic quantum states. In this work, we propose
a feasible approach to realize tunable nodal line connections in real
materials. We show that certain space group symmetries support the coexistence
of the planar symmetry enforced and accidental nodal lines, which are robust to
spin-orbit coupling and can be tailored into intricate patterns by chemical
substitution, pressure, or strain. Based on first-principles calculations, we
identify non-symmorphic centrosymmetric quasi-one-dimensional compounds,
K$_{2}$SnBi and MX$_{3}$ (M = Ti, Zr, Hf and X = Cl, Br, I), as materials
hosting such tunable 2D Dirac nodal nets. Unique Landau levels are predicted
for the nodal line semimetals with the 2D Dirac nodal nets. Our results provide
a viable approach for realize the novel physics of the nodal line connections
in practice.
