Maps of networks of stations currently contributing to (a) the Kp (and hence ap) index, (b) the am index and (c) the aa index. In each map, the light grey bands are typical locations of the auroral oval and dark grey bands are ideal middle geomagnetic latitudes for stations to give a K-index value, being close enough to give a large signal, but far enough away that the response is monotonic because, for all but the very largest disturbances, the auroral oval approaches the station as the activity level increases. Details of these stations, and others used in the past, are given in Appendix A. Images courtesy of the International Service of Geomagnetic Indices (ISGI).