The Source of Quantum Gravity presents the Pattern Field Theory (PFT) formulation of gravitation as a problem of transport architecture rather than the quantization of an already assumed gravitational geometry. The central structural result is 2D + 1D(n) ≡ interlayer identity coupling ≡ manifestation ≡ gravitation. In this construction, 2D denotes foundational non-interlayer transport, while 1D(n) denotes the depth-bearing cross-layer identity relation required for persistent manifestation. The additional relation is not treated as a third Cartesian spatial axis. Gravity is quantum at formation because interlayer identity coupling is constituted through discrete, rationically constrained event commitments; continuum gravity is the macroscopic aggregate expression of those commitments. The paper develops consequences for curvature, static and rotating gravitational systems, the Allen Orbital Lattice (AOL), Rationics and rationic budget, Logical Flow, Safe Equilibrium, Hamiltonian Differentiation and Hamiltonian Debt, Basin Dynamics, Equilibrion (EQUI), electromagnetic manifestation, Trishift, Settlement Horizons, Basin Edge Dynamics, black-hole information dynamics, cosmological structural continuity, and the PFT replacement of particulate dark matter. A quantitative galactic application is developed from the AOL ring architecture. Under explicitly stated asymptotic closure conditions, the ideal ring relation Nn=6nN_n=6nNn=6n produces an extended gext∝R−1g_{\mathrm{ext}}\propto R^{-1}gext∝R−1 response. The distinction between cumulative source growth and active source-boundary growth yields Vf4∝MbV_f^4\propto M_bVf4∝Mb, together with the asymptotic low-acceleration relation gext2∼aAOLgbarg_{\mathrm{ext}}^2\sim a_{\mathrm{AOL}}g_{\mathrm{bar}}gext2∼aAOLgbar. The paper further identifies the independently developed AOL Basel invariant π2/6\pi^2/6π2/6 as a candidate structural constraint on the remaining Initial Rationic Reference (IRR) normalization problem. The mapping between that invariant and the universal IRR handoff condition is explicitly retained as a derivation and falsification requirement rather than assumed. The work is presented as an Engineering Physics reference architecture with explicit structural dependencies, comparison with major quantum-gravity approaches, and an engineering test matrix.