Planetary Modelling via Hierarchical

In encoding, simplifying, amalgamating and intersecting cartographic features, it is useful to know the precision of locational data being processed. It is suggested that representing spatial phenomena in a hierarchical tessellated framework can facilitate documenting the certainty of coordinates and in dealing with its consequences. Objects thus encoded can identify the precision with which they were measured, and can retrieved at lower degrees of precision, as appropriate. This scale sensitivity is an inherent aspect of quadtree and pyramid data structures, and one which the literature on GIS data quality has yet to address in detail. A specific hierarchical tessellation of the sphere into triangular facets is proposed as a basis for indexing planetary data; Although composed of triangular facets, the tessellation is a quadtree hierarchy. Its geometry is such that that its facets are planar, subdivide a sphere naturally and are efficient to address. Methods for generating and manipulating hierarchical planetary geocodes are described. 1 Locational Data Quality Whatever else they may convey, all spatial data possess coordinate locations. Each geographic entity recorded in a GIS must have an identifiable spatial signature among its properties. As a GIS must be relied upon to integrate and analyze independent collections of spatial data, it should possess means for coping with variability in the quality of coordinate and other data in the features, layers and themes it records, according to their nature, source and purpose. This is usually not possible, hence rarely done. 1 Based on paper originally prepared for Specialist Meeting 1 for the first research initiative of the National Center for Geographic Information and Analysis, Santa Barbara, CA, Dec. 12-16,1988.