Использование баров из Google-графиков в качестве кнопок

Используйте событие "select":

google.visualization.events.addListener(chart, 'select', function () {
    var selection = chart.getSelection();
    if (selection.length > 0) {
        // then we selected something
        // most charts only support one selected element, so it is typically safe to do this:
        var row = selection[0].row;
        var column = selection[0].column;
        if (row == null) {
            // then someone clicked on the legend
        }
        else {
            // then someone clicked a chart element (bar, column, point, etc)
            // get any relevant data from the DataTable using the #getValue and/or #getFormattedValue methods
            // eg:
            var val = data.getValue(row, column);
            // do something with val
        }
    }
    else {
        // then we deselected all previously selected elements
    }
});