Abstract The problem of visualizing huge amounts of data is well known in Infor- mation Visualization. Dealing with a large number,of items forces almost any kind of Infovis technique to reveal its limits in terms of expressivity and scalability. In this paper we focus on 2D scatter plots, proposing a "feature preservation" approach, based on the idea of modeling the visu- alization in a virtual space in order to analyze its features (e.g, absolute density, relative density, etc.). In this way we provide a formal framework to measure the visual overlapping, obtaining precise quality metrics about the visualization degradation and devising automatic sampling strategies able to improve the overall image quality. Metrics and algorithms have been improved through suitable user studies. Keywords: overplotting, sampling, quality metrics, numerosity 2