Precise estimation of ionospheric time delay is essential for achieving better positional accuracy. The trans-ionospheric signals are affected due to the existence of anisotropic plasma in the ionosphere. For the first time, a novel model based on anisotropic Inverse Distance Weighting (IDW) with `Jackknife' technique is proposed and is applied in the context of ionospheric time delay modelling for Global Positioning System (GPS). The performance of the proposed anisotropic IDW model is evaluated by comparing with the prominent grid based models (Kriging, Spline and Modified Planar Fit (MPF)).