Information retrieval and visualization can be combined in dynamic query systems that allow users unparalleled access to information for decision making. In this paper, we report on the development and evaluation of a dynamic query system (YMap) that displays information on a chloropleth map using double thumb sliders to select ranges of query variables. The YMap prototype is a Java-Applet that supports panning and zooming. Several usability studies were conducted on early prototypes that resulted in the current version. Applications of YMap for decision making tasks are discussed.