Summary This chapter has presented an introductory overview of ground-based tomography. It has investigated the resolution and error sensitivity of a two-dimensional tomographic system and found that the full width at half maximum of the point spread function varies from 4 km at 120 km altitude to 10 km at 210 km altitude for an input point with side lengths of 2 km. It was discovered that the full width at 10 % of maximum was smeared out to all altitudes in the vertical direction. Together with the error sensitivity of the problem this implies that the result of the tomographic inversion cannot retrieve fine scale internal structures. However, estimates of the spatial distribution of ionospheric emissions which, in general, have a comparatively simple shape, can be accurately obtained. A strengthening of the statistical stopping criteria by Veklerov and Llacer (1989a) is presented.