We present a picture showing the magnetic topology and geometry of Ear
th's magnetotail and surrounding magnetosheath. The picture is constru
cted from a 4-year composite of magnetometer data from IMP 8. It repre
sent a cross-sectional plane around 30 R-e, tailward from Earth. It de
picts the situation that a quasi-equatorial interplanetary magnetic fi
eld produces, which is the common situation. It shows that the separat
rix between open and closed magnetic field lines lies in the boundary,
as expected. It shows that the tail is open tit high latitudes, also
as expected. However, it shows further that the tail is open along the
equatorial flanks, contrary to a standard assumption. That is, the pi
cture in which permanent, continuous boundary segments run along both
flanks separating closed field lines from fully disconnected field lin
es is inconsistent with the data.