S>It is proposed that the coronal source longitude and latitude of solar- wind plasma can be estimated within approximates 10 deg . Previous writers have argued that the solar wind in the ecliptic should originate near the equator and that a quasi-radial hypervelocity (QRH) approximation (constant radial flow) is valid beyond the magnetohydrodynamic critical points. It is demonstrated that an extension of the QRH approximation (as if the solar wind flowed radially with constant velocity from the center of the Sun) yields a proper estimate of the high coronal source location at the ( elease zone'' where the solar wind makes its transition to radial interplanetary flow, This extrapolated'' QRH (or EQRH) approximation succeeds because the two main corrections to this source estimate, coronal corotation and interplanetary acceleration, tend to cancel (the former correcting the source location eastward, the latter westward). Although this ideal spiral'' approximation was first suggested by Snyder and Neugebauer (1966), only recently has it been demonstrated that it relates a wide range of interplanetary plasma, magnetic fleld, and energetic particle data to observed coronal magnetic structure. The error in the EQRH approximation is estimated by comparison with steady-state streamlines predicted by azimuthally independent and dependent theoreticalmore » solutions to the steady-state plasma equations. The error in both cases <10 deg in longitude and it is therefore suggested that the EQRH approximation offers the means to relate observed solar initial conditions'' in the release zone'' directly to interplanetary measurements. If, in addition, the EQRH approximation also leads to agreement with low coronal structure, then there should be a straightforward correspondence to otherwise unobservable high coronal structure. (auth)« less