Introduction

Particularly at the shorter wavelengths, the ALMA will need to do mosaic observing to cover large fields of view. Along with the mosaic pointing, there will need to be total power maps to fill in the interferometric short spacings and produce complete images. It is well known that this is best done with a single antenna that is two to three times the diameter of the interferometer antennas (Vogel,S.$\it et \it al$, ApJ, 1984, 283, 655). However, that will not be possible for ALMA; there are no 24m - 36m antennas available that will work well to 0.35mm wavelength. As long as a mosaic of pointings is employed in the interferometry, a single antenna map made with one of the interferometer antennas will suffice in principle (Ekers,R. and Rots,A, 1979, In Image Formation, etc., Dordrecht, Reidel). This is rarely done, largely because the interferometer antennas are not equipped to do it. Tests done at the VLA at cm wavelengths (Cornwell, T. 1988, A&A, 202, 316.) indicate that it should work, and at mm wavelengths in the CO(1-0) line, Marc Pound made a good map of the Eagle Nebula combining a Mosaic interferometer map made with the BIMA array and a single antenna map made with the Bell Labs 7m antenna (Pound, 1998, ApJ, 493L, 113). This capability must be in place for the ALMA antennas. How it is best done may be studied with the prototype antennas.