This paper investigates the spatiotemporal frequency distribution characteristics induced by high-penetration converter-interfaced generation, with the aim of precisely characterizing the underlying dynamics and quantifying nodal frequency heterogeneity under massive converter integration. First, a multi-machine multi-node frequency response model is developed by integrating electromagnetic power interactions with nodal frequency dynamics. This model embeds power-frequency dynamic equations of both GFL(Grid-Following) and GFM(Grid-Forming) converters, enabling precise characterization of frequency coupling mechanisms across heterogeneous nodes. Second, a comprehensive spatiotemporal frequency index set is proposed, including the Spatiotemporal Consistency Coefficient of Frequency Nadir, the Dynamic Weighted Entropy of Frequency Standard Deviation and the Node Quasi-Steady-State Frequency Synchronization Coefficient. These indices collectively establish an integrated assessment framework for evaluating transient frequency security margins and spatiotemporal distribution patterns. Finally, the effectiveness of the proposed model and methodology is verified through multi-scenario case simulations.