Traditional inertia estimation techniques, which assume a fixed and centralized inertia distribution, are becoming less effective due to the spatial variability introduced by renewable energy sources. This study proposes an inertia estimation method using a polynomial fitting approach to improve estimation accuracy by analyzing frequency and power deviations at multiple system buses. The method is tested on the Kundur two-area system and the IEEE 39-bus system, where disturbances are introduced at different locations to assess spatial inertia variations. The results indicate that estimation errors are highest at the faulted buses and decrease progressively with distance from the disturbance.