Bivariate boxplot: A bivariate analogue of boxplot in which the inner area contains 50%of the data, and a 'fence' helps to identify the potential outliers. Robust methods or techniques are usually used to ?nd out the estimates of the location, scale and correlation parameters needed to construct the plot, so as to avoid possible distortions which outlying observations might cause. An instance of such a plot for number of manufacturing enterprises and sulphur dioxide concentration recorded for the number of cities in USA with cities deemed outliers labeled with the name of city.