  We present a study of ultra compact dwarf (UCD) galaxies in the Virgo cluster
based mainly on imaging from the Next Generation Virgo Cluster Survey (NGVS).
Using $\sim$100 deg$^{2}$ of $u^*giz$ imaging, we have identified more than 600
candidate UCDs, from the core of Virgo out to its virial radius. Candidates
have been selected through a combination of magnitudes, ellipticities, colors,
surface brightnesses, half-light radii and, when available, radial velocities.
Candidates were also visually validated from deep NGVS images. Subsamples of
varying completeness and purity have been defined to explore the properties of
UCDs and compare to those of globular clusters and the nuclei of dwarf galaxies
with the aim of delineating the nature and origins of UCDs. From a surface
density map, we find the UCDs to be mostly concentrated within Virgo's main
subclusters, around its brightest galaxies. We identify several subsamples of
UCDs -- i.e., the brightest, largest, and those with the most pronounced and/or
asymmetric envelopes -- that could hold clues to the origin of UCDs and
possible evolutionary links with dwarf nuclei. We find some evidence for such a
connection from the existence of diffuse envelopes around some UCDs, and
comparisons of radial distributions of UCDs and nucleated galaxies within the
cluster.
