The city has the largest population in the country and 'in addition' [='also, additionally'] is a major shipping port.
an 'addition to' the family [=a new member of the family, such as a newborn baby]
The soup was thickened by the 'addition of' cream in the last stage of cooking.
(..) I'm thrilled for you both. This is a heck of a decision. You have my full support. Okay. I think it'll be a perfect addition to the family. I know I'll love the heck out of the little bugger. I'm just hoping that little one over there doesn't get jealous. Oh, this little one (..)2012 TvShow: Modern Family Title: Bringing Up Baby Season: 4 Episode 1