Subsampling coupled with intensitytapering may suppress, to some extent, cluttering and convey the flow orientation (the positive direction of the field) while a rainbow color map can be adopted to show the velocity magnitude. As an alternative, colorwheel maps flow vectors to HueSaturationValue (HSV) colors through the use of a legend where there are a onetoone correspondence between normalized vectors and circularly distributed radial lines of hue and a certain map between magnitude and radially varying brightness or value. Arrows are a little bit more complex in geometry than intensitytapering line segments and hence require sparser subsampling of the field to alleviate the cluttering problem. Arrowsize mapping, in addition to the aforementioned two color map schemes, can be employed to depict the velocity magnitude. Sometimes arrows are placed at jittered grid points in a way to combat artifacts that would otherwise result from the regular pattern of the underlying grid. However, cavities might occur near flow boundaries. 
Fixedsize arrows at regular grid
points

Variablesize arrows at regular
grid points

Variablesize arrows at jittered
grid points

Variablesize arrows at regular
grid points
