This mod change sea-level and make many small islands.
Explore in the new Islands-world, world of many small islands!

Recommended

When there is a way to cross a sea, it's somewhat convenient.

Beautiful Bridge Railway is balanced for this mod.
https://mods.factorio.com/mods/kapaer/beautiful_bridge_railway

Biters do not attack across the ocean, but if you want them to do it, the following MOD is recommended.
Noxys Swimming
Allows you to "Swim" through water slowly and Biters will attack across the ocean.

Others, several vehicle mods (aircraft, ship etc.) would be your help.

Ships
https://mods.factorio.com/mod/ships_extended

Aircraft
https://mods.factorio.com/mod/Aircraft
Helicopters
https://mods.factorio.com/mod/Helicopters
Raven
https://mods.factorio.com/mod/Raven

Usage

It's OK even just as it is, but when set Map-preset as "Many islands", a better result is obtained.
I recommended to set resource-frequency and size highly, because much inside the resources goes off in the sea.
The resources added by other mods (Angel's, Bob's etc.) are setting of default, so please change it manually.

Rarely, start island has no necessary resources. Please re-generate map.

Before 0.17 only:
Please enable this mod in the new game, DO NOT use in the middle of the game that was started before the enabling.
When you enable it in the middle of the game that was started before the enabling, step will be generated in the newly opened region.
If you disable it once after enabling and starting, step will occur in the region opened during that time.