The optimum spatial resolution of APT is estimated to be better than 0.06 nm in depth (z) and the lateral resolution (x, y) below 0.2 nm. However, several factors can affect the spatial resolution.
Variations in the local geometry and composition on the surface of the tip can cause trajectory aberrations in the flight path, degrading the spatial resolution.
The effect of atoms moving at the surface of the tip just before field ionisation is known as surface migration and is a limiting factor for spatial resolution.

Schematic showing inhomogeneity in the surface topology causing trajectory aberations.

Trajectory aberrations, such as local magnification, can occur as a result of the tip becoming mis-shaped by the retention of, for example, a high field precipitate. Local magnification effects usually involve preferential evaporation or non-evaporation of particular elements that require a higher field of evaporation than the rest of the surface. This can be seen in the image below. This typically occurs when precipitates are present, and It results in a non-uniform sequence of evaporation, which is detrimental for the spatial resolution.

Schematic showing different evaporation fields causing trajectory aberations.

Finally, the overall accuracy of an APT experiment is limited by the reconstruction algorithm. Since the reconstruction is not perfect (the assumptions it is based on do not always hold true), it is therefore a source of error in atom probe datasets.