Streamlines are a family of curves that are instantaneously tangent to the velocity vectors in a flow field. They show the direction toward which a fluid element will travel at any point in time.
Streamlines represent the instantaneous direction of the wind and are drawn as unending lines that may converge or diverge from one another (following specific rules). They are drawn at roughly even intervals to capture the flow in all areas. Thus, the distance between streamlines is not generally representative of any gradient or proportional to wind speed.