  We present the largest catalog to-date of star clusters and compact
associations in nearby galaxies. We have performed a V-band-selected census of
clusters across the 38 spiral galaxies of the PHANGS-HST Treasury Survey, and
measured integrated, aperture-corrected NUV-U-B-V-I photometry. This work has
resulted in uniform catalogs that contain $\sim$20,000 clusters and compact
associations which have passed human inspection and morphological
classification, and a larger sample of $\sim$100,000 classified by neural
network models. Here, we report on the observed properties of these samples,
and demonstrate that tremendous insight can be gained from just the observed
properties of clusters, even in the absence of their transformation into
physical quantities. In particular, we show the utility of the UBVI color-color
diagram, and the three principal features revealed by the PHANGS-HST cluster
sample: the young cluster locus, the middle-age plume, and the old globular
cluster clump. We present an atlas of maps of the 2D spatial distribution of
clusters and compact associations in the context of the molecular clouds from
PHANGS-ALMA. We explore new ways of understanding this large dataset in a
multi-scale context by bringing together once-separate techniques for the
characterization of clusters (color-color diagrams and spatial distributions)
and their parent galaxies (galaxy morphology and location relative to the
galaxy main sequence). A companion paper presents the physical properties:
ages, masses, and dust reddenings derived using improved spectral energy
distribution (SED) fitting techniques.
