Being Van Kampen is a universal property
  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. 
Pawel Sobocinski (DSSE, ECS, University of Southampton), Tobias   Heindel (Laboratoire d'Informatique de Paris-Nord, Univers...
math.CT cs.PL