visualizations context query

I am displaying a chart which has region like New York, Boston, Atlanta etc on it ‘X’ axis and their corresponding revenue on the ‘Y’ axis. Now on click of a particular region i want to open up a popup and only show data details specific to that region. When i set the name of the region in the context of the pop-up no data is displayed. The context is mapping the value of the region with the id. How can i map it with any other field?

So i added the region field instead of id by editing the xml. Now it is showing data for all the region on the pop-up irrespective of which region i click on on the graph.

Do want to mention. The model of the pop-up is different from model of the chart because the pop-up model is an aggregate