  Context. Protoplanetary disks show large diversity regarding their morphology
and dust composition. With mid-infrared interferometry the thermal emission of
disks can be spatially resolved, and the distribution and properties of the
dust within can be studied. Aims. Our aim is to perform a statistical analysis
on a large sample of 82 disks around low- and intermediate-mass young stars,
based on mid-infrared interferometric observations. We intend to study the
distribution of disk sizes, variability, and the silicate dust mineralogy.
Methods. Archival mid-infrared interferometric data from the MIDI instrument on
the VLTI are homogeneously reduced and calibrated. Geometric disk models are
used to fit the observations to get spatial information about the disks. An
automatic spectral decomposition pipeline is applied to analyze the shape of
the silicate feature. Results. We present the resulting data products in the
form of an atlas, containing N band correlated and total spectra, visibilities,
and differential phases. The majority of our data can be well fitted with a
continuous disk model, except for a few objects, where a gapped model gives a
better match. From the mid-infrared size--luminosity relation we find that
disks around T Tauri stars are generally colder and more extended with respect
to the stellar luminosity than disks around Herbig Ae stars. We find that in
the innermost part of the disks ($r \lesssim 1$~au) the silicate feature is
generally weaker than in the outer parts, suggesting that in the inner parts
the dust is substantially more processed. We analyze stellar multiplicity and
find that in two systems (AB Aur and HD 72106) data suggest a new companion or
asymmetric inner disk structure. We make predictions for the observability of
our objects with the upcoming MATISSE instrument, supporting the practical
preparations of future MATISSE observations of T Tauri stars.
