Grand Temple:Unable to understand question
Hey Nilesh, in this problem co-ordinates denote the river which is flowing through the point horizontally as well as vertically. And you have to find the largest area which we can get. Just one thing to remember when you are calculating an area is area will be calculated between the edge next to the left edge, the edge above the bottom edge, the topmost edge and the rightmost edge.
For getting it more clearly you can draw this for the given example in the problem.
Hope this helps you 
So,Basically you just need to find maximum difference in X coordinates (let’s say max_x) and same for y coordinates (let’s say max_y) then your answer will be max_x*max_y .Just keep in mind that there is many river too .