Isotachs

http://www.ssec.wisc.edu/media/April2003.html
Isotachs as pictured above are lines on a weather map or chart that connect points where winds of equal speeds have been recorded. An isotach is a type of contour line used on meteorological maps for demonstrating wind speed. This image is of part the Pacific Ocean and was produced in January 29, 2003 from a satellite orbiting Earth called GOES-10; the Isotachs are an overlay.