Visual exploration systems enable users to search, browse, and explore voluminous multimedia databases in an interactive and playful manner. Whether users know the database's contents in advance or not, these systems guide the user's exploration process by visualizing the database contents and allowing him or her to issue queries intuitively. In order to improve the efficiency of content-based visual exploration systems, we propose an efficient query evaluation scheme which aims at reducing the total number of costly similarity computations. We evaluate our approach on different state-ofthe-art image databases. Keywords-content-based multimedia exploration; visual exploration; similarity-based visualization; efficient query processing