  The reconstruction problem in electrical impedance tomography is highly
ill-posed, and it is often observed numerically that reconstructions have poor
resolution far away from the measurement boundary but better resolution near
the measurement boundary. The observation can be quantified by the concept of
distinguishability of inclusions. This paper provides mathematically rigorous
results supporting the intuition. Indeed, for a model problem lower and upper
bounds on the distinguishability of an inclusion are derived in terms of the
boundary data. These bounds depend explicitly on the distance of the inclusion
to the boundary, i.e. the depth of the inclusion. The results are obtained for
disk inclusions in a homogeneous background in the unit disk. The theoretical
bounds are verified numerically using a novel, exact characterization of the
forward map as a tridiagonal matrix.
