Maritime (14)
http://www.worldheritagesite.org/categories/category32.html

Angra
Bryggen
Cartagena
Hoi An
Mozambique
Karlskrona
Luebeck
Liverpool
Macao
Greenwich
Oporto
Stralsund and Wismar
Valparaiso
Visby

I would also add Hamburg for its Speicherstadt.

My selection:

Cartagena
Hoi An
Karlskrona
Macao
Greenwich
Stralsund and Wismar

Hmm. I would limit it to:

Cartagena - representing world exploration and the great commercial maritime routes.
Lübeck - representing the Hanseatic League
Maritime Greenwich - represents the development of navigation and astronomy

I limit only to Cartagena.

Greenwich has to be included for it architecture and role in navigation, GMT, astronomy etc
Brygen - I am suprised this hasn't received any support. OK it is a bit touristy but it seems to me to better represent a late mediaeval port and the Hanseatic League etc than any other?
Cartagena - OK as stated
Liverpool or Hamburg. Which better represents later maritime cities. There should be one of these I feel?

My selection:

Bryggen (one of the best cultural sites in Scandinavia)
Lubeck (hanseatic league)
Greenwich (but won't make my top 200)
Cartagena
Venice I feel is the maritime city par excellence so I wouldn't include Liverpool or Hamburg
Oporto (maybe, as a great example in the Iberian peninsula and as it could also represent the importance of the Douro wine indirectly)

Summarizing:

Angra
Bryggen - to represent a late mediaeval port and the Hanseatic League
Cartagena - representing world exploration and the great commercial maritime routes
Hoi An
Mozambique
Karlskrona
Luebeck - representing the Hanseatic League
Liverpool
Macao
Greenwich - represents the development of navigation and astronomy
Oporto
Stralsund and Wismar
Valparaiso
Visby

my selectin:

Hoi An
Liverpool
Greenwich

Ah - so Cartagena is hiding here!
Ok, I would support that too. Greenwich as well, for the reasons stated.
In addition, I would add my support to Lübeck - the most emblematic Hanseatic city.

Here there are two in favour of Hoi An which should be raised into cursive.

Summarizing again, these are already included in the main summary at http://www.worldheritagesite.org/allbyrank.php:

Angra
Bryggen - to represent a late mediaeval port and the Hanseatic League
Cartagena - representing world exploration and the great commercial maritime routes
Hoi An -
Mozambique
Karlskrona
Luebeck - representing the Hanseatic League
Liverpool
Macao
Greenwich - represents the development of navigation and astronomy
Oporto
Stralsund and Wismar
Valparaiso
Visby