  The fields of view of Extremely Large Telescopes will contain vast numbers of
spatial sampling elements (spaxels) as their Adaptive Optics systems approach
the diffraction limit over wide fields. Since this will exceed the detection
capabilities of any realistic instrument, the field must be dilutely sampled to
extract spectroscopic data from selected regions of interest. The scientific
return will be maximised if the sampling pattern provides an adaptable
combination of separated independent spaxels and larger contiguous sub-fields,
seamlessly combining integral-field and multiple-object spectroscopy. We
illustrate the utility of this Diverse Field Spectroscopy (DFS) to cosmological
studies of galaxy assembly. We show how to implement DFS with an instrument
concept: the Celestial Selector. This integrates highly-multiplexed monolithic
fibre systems (MFS) and switching networks of the type currently available in
the telecommunications industry. It avoids bulky moving parts, whose
limitations were noted in Paper I. In Paper III we will investigate the
optimisation of such systems by varying the input-output mapping.
