  Several ongoing international efforts are developing methods of localizing
single cells within organs or mapping the entire human body at the single cell
level, including the Chan Zuckerberg Initiative's Human Cell Atlas (HCA), and
the Knut and Allice Wallenberg Foundation's Human Protein Atlas (HPA), and the
National Institutes of Health's Human BioMolecular Atlas Program (HuBMAP).
Their goals are to understand cell specialization, interactions, spatial
organization in their natural context, and ultimately the function of every
cell within the body. In the same way that the Human Genome Project had to
assemble sequence data from different people to construct a complete sequence,
multiple centers around the world are collecting tissue specimens from a
diverse population that varies in age, race, sex, and body size. A challenge
will be combining these heterogeneous tissue samples into a 3D reference map
that will enable multiscale, multidimensional Google Maps-like exploration of
the human body. Key to making alignment of tissue samples work is identifying
and using a coordinate system called a Common Coordinate Framework (CCF), which
defines the positions, or "addresses", in a reference body, from whole organs
down to functional tissue units and individual cells. In this perspective, we
examine the concept of a CCF based on the vasculature and describe why it would
be an attractive choice for mapping the human body.
