No abstract

Traditional multivariate clustering approaches are common in many geovisualization applications. These algorithms are used to define geodemographic profiles, ecosystems and various other land use patterns that are based on multivariate measures. Cluster labels are then projected onto a choropleth map to enable analysts to explore spatial dependencies and heterogeneity within the multivariate attributes. However, local variations in the data and choices of clustering parameters can greatly impact the resultant visualization. In this work, we develop a visual analytics framework for exploring and comparing the impact of geographical variations for multivariate clustering. Our framework employs a variety of graphical configurations and summary statistics to explore the spatial extents of clustering. It also allows users to discover patterns that can be concealed by traditional global clustering via several interactive visualization techniques including a novel drag & drop clustering difference view. We demonstrate the applicability of our framework over a demographics dataset containing quick facts about counties in the continental United States and demonstrate the need for analytical tools that can enable users to explore and compare clustering results over varying geographical features and scales.

We have investigated the stability of ensembles of Ge/Si(100) islands by annealing at their growth temperature. Islands grown by molecular beam epitaxy at temperatures of 450, 550, 600 and 650°C were annealed for times between 5 and 120 minutes. Small, pure Ge hut clusters, bound by {105} facets appear to be extremely stable structures, surviving the longest anneals with no apparent coarsening. Dome clusters, however, coarsen. Large alloyed hut clusters, apparent in as-grown samples only for growth temperatures greater than 600°C, appear during annealing at 450 and 550°C. During anneals at 550 and 650°C, we observe novel coarsening behavior. Arrays of crystallographically oriented, alloyed hut clusters are formed which result from the dissolution of large, alloyed dome clusters.