This map illustrates how the addition of the Virgo detector, scheduled to come online this summer, could improve the localization of sources of gravitational waves. The map shows the estimated locations of the four black-hole merger events detected by LIGO to date (including one event seen at lower significance), after including hypothetical Virgo data. Outer contours represent the 90 percent confidence region; innermost contours signify the 10 percent confidence region.