Northern Hemisphere Maps of Cyclone Tracks is a historical digital data set DSI-9629 that is archived at the National Climatic Data Center (NCDC). This reference manual was prepared for use with punched card deck 623, Northern Hemisphere Pressure Center Track Data. These cards were punched from data encoded from pressure center track maps, derived from the 40-year series, Northern Hemisphere ... Historical Map Series, source 005. Maps of the trajectories of all pressure centers were prepared from the map series, for the period January 1899 through June 1939. The track maps were prepared for lows and highs separately by decades, with a two-day overlap between adjacent maps. Thus, six track maps, three for highs and three for lows, summarized all the pressure center tracks in the Northern Hemisphere for any given month during the period of record. From these track maps were coded the date, location, serial number, intensity, direction of movement, orientation of major axis, type of low pressure center (highs were not sub-divided into types), speed of movement during the past 24 hours, speed of movement during the following 24 hours, and the acceleration during the 48 hours.