The interactive map PaperScape [paperscape.org] by high energy physics researcher Damien George and particle physics PhD student Rob Knegjens provides a visual overview of all the 869,258 scientific physics, mathematics, and computer papers that have been published at open e-print archive arXiv.
Each paper is represented by a circle, of which the surface area is proportional to the number of citations that paper has received. The color of each circle denotes the arXiv category of the paper, while the brightness indicates age. The text labels have been automatically extracted by analysing the word frequency in the title and abstract of each paper, and are generally indicative of the subject matter.
More technical explanation about this project can be found here.