The divergence measures the net outward flux per unit area at each point. Positive = source (fluid created). Negative = sink (fluid destroyed). Zero = incompressible.
Highlight regions by the sign of divergence. Where fluid is created, compressed, or neither.
The total outward flux through a closed curve equals the integral of divergence over the enclosed region. This works because the interior contributions telescope — adjacent cells share boundaries where flux cancels.
Arrows show the field direction & magnitude (color = speed: blue→red).
Particles trace out flow lines — their trails reveal trajectories.