Around Orca Island you'll be able to find a lot of road-signs scattered around, that will give you information about where you're heading. Also as of patch #31, an In-Game map has been added, a map that you can actually find in the world, and equip it in your hands, to navigate with.
That's how it looks like while it's equipped in your hands: http://imgur.com/EGwd70d
And that's how it looks like when it spawns in the world: http://imgur.com/gTeLeVg
The red colors on the map are only temporary, as they currently mark the "end" of the map, which is stil being worked on actively by the level designers.
The real map
Another ingame map found as a sign near the beach.
Size of World
Source: Miscreated - Twitch.tv Stream - Latest Game Progress, General Q&A from 10-27-2014
Currently the map is 8km x 8km, giving a total area of 64² km. Currently, only about 50% of the map has been completed. In order to avoid players ending up in a vast desolate wasteland before content has been created, invisible walls have been implemented. The eventual plan is to remove and/or relocate these invisible walls as more of the world is fleshed out.
In-game Map
Since the last updates, the game is now furnished with an equippable in game map! This map can be put in one of the belt slots and the player can equip it by pressing the corresponding key(5/6). Also, the player can consult it using his first person view.
You can also consult the map here.
Guided Tour of Current Map (11-18-2014)
LCBradley3k has posted this guided tour of the map on YouTube.