The original intent of the study was to develop a first-order synopsis of island hydrology with an integrated geologic basis on a global scale. As the study progressed, the aim was broadened to provide a framework for subsequent assessments on large regional or global scales of island resources and impacts on those resources that are derived from global changes.
Fundamental to the study was the development of a comprehensive framework?a wide range of parameters that describe a set of 'saltwater' islands sufficiently large to
Characterize the spatial distribution of the world?s islands;
Account for all major archipelagos;
Account for almost all oceanically isolated islands, and
Account collectively for a very large proportion of the total area of the world?s islands whereby additional islands would only marginally contribute to the representativeness and accountability of the island set.
The comprehensive framework, which is referred to as the ?Primary Island Set,? is built on 122 parameters that describe 1,000 islands. To complement the investigations based on the Primary Island Set, two supplemental island sets, Set A?Other Islands (not in the Primary Island Set) and Set B?Lagoonal
Atolls, are included in the study.
The Primary Island Set, together with the Supplemental Island Sets A and B, provides a framework that can be used in various scientific disciplines for their island-based studies on broad regional or global scales.
The study uses an informal, coherent, geophysical organization of the islands that belong to the three island sets. The organization is in the form of a global island chain, which is a particular sequential ordering of the islands referred to as the 'Alisida.'
The Alisida was developed through a trial-and-error procedure by seeking to strike a balance between 'minimizing the length of the global chain' and 'maximizing the chain?s geophysical coherence.' The fact that an objective function cannot be minimized and maximized simultaneously indicates that the Alisida is not unique. Global island chains other than the Alisida may better serve disciplines other than those of hydrology and geology.
Additional publication details
USGS Numbered Series
Habitat and environment of islands: primary and supplemental island sets