If the divergence $$\nabla \cdot \boldsymbol{F}$$ of a vector field $$\boldsymbol{F}$$ at location $$(x,y,z)$$ is positive:$\nabla \cdot \boldsymbol{F}(x,y,z) ~>~ 0$then there is a source of the vector field at the location $$(x,y,z)$$. If this location is enclosed with an arbitrary surface, then the vector field 'flows' out of the surface.