The times of maximum velocity of high-speed streams in the solar wind are used to organize the analysis of planetary geomagnetic activity index Ap, and this organization of the data is shown to give a clearer pattern than the organization of the data around sector boundaries. Geomagnetic activity is highest on the day preceding peak velocity in the high-speed stream. The sector boundary analysis confirms the minimum in geomagnetic activity preceding sector boundary crossing found by Shapiro (1974) but shows little dependence on the sense of the boundary.