  Colimits that satisfy the Van Kampen condition have interesting exactness
properties. We show that the elementary presentation of the Van Kampen
condition is actually a characterisation of a universal property in the
associated bicategory of spans. The main theorem states that Van Kampen cocones
are precisely those diagrams in a category that induce bicolimit diagrams in
its associated bicategory of spans, provided that the category has pullbacks
and enough colimits.
