Overlap Removal of Dimensionality Reduction Scatterplot Layouts

Dimensionality Reduction (DR) scatterplot layouts have become a ubiquitous visualization tool for analyzing multidimensional data items with presence in different areas. Despite its popularity, scatterplots suffer from occlusion, especially when markers convey information, making it troublesome for users to estimate items' groups' sizes and, more importantly, potentially obfuscating critical items for the analysis under execution. Different strategies have been devised to address this issue, either producing overlap-free layouts, lacking the powerful capabilities of contemporary DR techniques in uncover interesting data patterns, or eliminating overlaps as a post-processing strategy. Despite the good results of post-processing techniques, the best methods typically expand or distort the scatterplot area, thus reducing markers' size (sometimes) to unreadable dimensions, defeating the purpose of removing overlaps. This paper presents a novel post-processing strategy to remove DR layouts' overlaps that faithfully preserves the original layout's characteristics and markers' sizes. We show that the proposed strategy surpasses the state-of-the-art in overlap removal through an extensive comparative evaluation considering multiple different metrics while it is 2 or 3 orders of magnitude faster for large datasets.Comment: 11 pages and 9 figure

Riqueza e abundância de herbívoros em flores de Vellozia nivea (Velloziaceae) Richness and abundance of herbivores on Vellozia nivea (Velloziaceae) flowers

Vellozia nivea (Velloziaceae) é planta de porte herbáceo que ocorre em solos rochosos, nos campos rupestres da Serra do Cipó, MG. Suas flores hermafroditas são extremamente macias, representando fonte tenra de alimento para os insetos que predam suas tépalas e estruturas reprodutivas. Este trabalho teve como objetivo observar a influência da altura e do número de flores da planta hospedeira na abundância e riqueza de insetos herbívoros. Foram encontradas o total de 21 morfoespécies de insetos (nove famílias e três ordens) associadas às flores de V. nivea. A altura e o número de flores da planta não apresentaram correlações significativas com a riqueza de herbívoros por planta (r² = 0,17; P > 0,05). Entretanto, estes dois fatores juntos explicaram 39% da variação observada na abundância dos insetos herbívoros por planta (P < 0,05). Portanto, o número de flores e a altura das plantas hospedeiras influenciaram apenas a abundância dos herbívoros.<br>Vellozia nivea (Velloziaceae) is a herbaceous plant that occurs on rocky soils in the rupestrian fields of the "Serra do Cipó", Minas Gerais State, Brazil. Its hermaphrodite flowers are extremely soft, representing a source of tender food for the insects that prey on its tepals and reproductive structures. The aim of this study was to observe the effect of the height and number of flowers of the host plant on the abundance and richness of herbivorous insects. We found 21 morphospecies of insects (nine families and three orders) associated to flowers of V. nivea. No significant correlation between the number of flowers and plant height and the variety of herbivorous insects per plant was observed (r² = 0.17, P > 0.05). However, these two factors together explained 39% of the variation of insect abundance (P < 0.05). Thus, only the abundance of herbivorous insects was influenced by the number of flowers and the height of host plant