  HEALPix -- the Hierarchical Equal Area iso-Latitude Pixelization -- is a
versatile data structure with an associated library of computational algorithms
and visualization software that supports fast scientific applications
executable directly on very large volumes of astronomical data and large area
surveys in the form of discretized spherical maps. Originally developed to
address the data processing and analysis needs of the present generation of
cosmic microwave background (CMB) experiments (e.g. BOOMERanG, WMAP), HEALPix
can be expanded to meet many of the profound challenges that will arise in
confrontation with the observational output of future missions and experiments,
including e.g. Planck, Herschel, SAFIR, and the Beyond Einstein CMB
polarization probe. In this paper we consider the requirements and constraints
to be met in order to implement a sufficient framework for the efficient
discretization and fast analysis/synthesis of functions defined on the sphere,
and summarise how they are satisfied by HEALPix.
