Group III-nitride materials have drawn a great deal of renewed interest due to their versatile characteristics as quantum emitters including room-temperature operation, widely tunable wavelengths from ultraviolet to infrared, and a high degree of linear polarization. However, most reported results for III-nitride-based quantum emitters show large inhomogeneous line width broadening in comparison to their lifetime-limited values, which is detrimental to achieving indistinguishability with high visibility. To overcome this, we propose an unprecedented InGaN quantum dot formation technique at the apex of GaN nanopyramid structures, which significantly suppresses inhomogeneous line width broadening. Using high-resolution transmission electron microscopy, a site controlled InGaN quantum dot with small height (<2 nm) was estimated. No measurable screening effect or frequency jitter of the single-photon emission was observed, which leads to the narrow homogeneous emission line width (64 +/- 8 mu eV) beyond the spectral resolution limit via Fourier-transform spectroscopy. The emitted photons exhibited superb antibunching characteristics with a near-unity degree of linear polarization, which is highly relevant for polarized nonclassical light sources for applications in quantum information processing.