== Largest Corporation can be concocted  == 

 But largest city as defined by census cannot be.  It counts urban area defined by inhabitation, not by the boundaries political parties change to suit their needs. 
 Kochi has a vast urban area surrounding it. That is, even in if Kochi corporation expands to 150 sqkm, it will have more population than Trivandrum with its 194 sqkm. Political parties try to gerrymander boundaries, for example CPM tries to add more panchayats to Trivandrum (mind you, panchayats not even municipalities !!) Congress opposes this as it will affect them adversely in terms of electoral politics. But Congress-ruled Kalamassery regularly opposes its merger with Kochi, claiming that it will lead to increase in taxes (real reason is that they will lose hold over the power).  This is a omnipresent phenomena.  This is why census people have differentiated between urban area and corporation limits.  Former is technical - decided by population density while latter is decided 
 by manipulation.  Hence when we talk of a city, we talk about technical term not the political administrative set up.