All locations on the Blue Sea are broken up and enlisted below.
Blue Sea
East Blue
Going by what Mihawk said when he first met the Straw Hat Pirates East Blue is the weakest of the four Blue´s. And it is the one of them about which has been shown the most so far. This is of course because the story starts there. All of the places that have been shown of East Blue are listed below. Those that have been visited by the any of the Straw Hats and those that weren´t so far.
Places already visited by a Straw Hat Pirate:
Since Luffy himself comes from East Blue and meets Zoro, Nami, Usopp and Sanji here, there are some places in East Blue that were visited by a Straw Hat Pirate. They list as follows:
Places not yet visited by a Straw Hat Pirate:
West Blue
It is not clear how weak or strong West Blue is actually. But since East Blue is the weakest of the four Blue´s it´s clear that West Blue is stronger then this one. The little amount of West Blue places that have been shown or mentioned so far are listed below.
Places already visited by a Straw Hat Pirate:
Unlike East Blue West Blue is not place where the Straw Hat Pirates were traveling so far. However right now the manga is telling Nico Robin's past which took place in West Blue. Which gives this sea a little bit of a familiar flair. The only known place that falls under that category so far is:
Places not yet visited by a Straw Hat Pirate:
North Blue
It is not clear how weak or strong North Blue is actually. But since East Blue is the weakest of the four Blue's, it's clear that North Blue is stronger then this one. The little amount of North Blue places that have been shown or mentioned so far are listed below.
Places already visited by a Straw Hat Pirate:
So far there's no place been introduced that was visited by any of the Straw Hat Pirates. However Sanji himself said that he comes from North Blue so it is clear that there must be at least one place he's been to there. That's all the information that exists about it for now. It that should change at some point, it'll be mentioned here.
Places not yet visited by a Straw Hat Pirate:
South Blue
It is not clear how weak or strong South Blue is actually. But since East Blue is the weakest of the four Blue's, it's clear that South Blue is stronger then this one. The little amount of South Blue places that have been shown or mentioned so far are listed below.
Places already visited by a Straw Hat Pirate:
So far there´s no place been introduced that was visited by any of the Straw Hat Pirates. It that should change at some point, it'll be mentioned here.
Places not yet visited by a Straw Hat Pirate:
Calm Belt
Judging from the maps shown so far it appears that there are islands within the Calm Belt however not a single one of them has been mentioned so far. However since the Straw Hat Pirates went into the Calm Belt for a short period it counts as a place they've been to.
Places already visited by a Straw Hat Pirate:
Places not yet visited by a Straw Hat Pirate:
None been mentioned so far. It that should change at some point, it'll be mentioned here.
Red Line
Since the Red Line is a continent it is very likely that there's lots of places where people live. However not a single one of such places has been shown nor was anything about such places mentioned so far. So there's also the possibility that the entire Red Line is unpopulated. Hopefully something more will be explained about it at some point.
Places already visited by a Straw Hat Pirate:
Places not yet visited by a Straw Hat Pirate:
None been mentioned so far. It that should change at some point, it'll be mentioned here.
Grand Line
The Grand Line is the main area where the story takes place. It is the most dangerous sea in the world because of the climatic conditions and because of all the strong people that live there or sail this sea. Also the World Government seems to have mostly present on this area of the world and even the Marine Headquarters seems to be based there somewhere. All in all there's many places that have been shown in the Grand Line so far, both such that have been visited by the Straw Hat Pirates so far and those that weren't.
Places already visited by a Straw Hat Pirate:
Places not yet visited by a Straw Hat Pirate: