A line in a given surface connecting points with equal wind speed. Also known as isokinetic; isovel.
A line on a weather chart showing equal, or constant, wind speed. These are generally drawn on high-level charts, generally 500 millibars and higher. These are short dashed lines labeled in knots and are normally indicated for intervals of 20 knots, where space permits. Isotachs, however, do not indicate wind direction.