Once you’ve made a few levels, you might start thinking about making a complete chapter, before we start let's define some stuff and clear up a few misconceptions.

Chapter: A collection of levels, usually with a similar theme or graphics style.

Map Level: A level which defines and arranges the level buttons for a chapter.

Island: The game’s mechanism for creating a Chapter, linking a Map level and the list of levels in the Chapter.
An island is defined in the [ island.xml ] file.

Island and Chapter Numbers

There are 5 islands (1 -> 5) ignoring the mythical / non-functional Island6

There is no connection between Chapter Number and Island Number… the Chapter Number shown for any island is just specified as text in the Global Text file.
OK… 2DBoy set up the original in the "sensible" way; Chapter 1 uses Island1, Chapter 2 uses Island 2 etc.
However there is no absolute need to do this, the Chapter assigned to Island1 can be given any number in its title text.

Open Chapters and Pointer Arrows in MapWorldView

There is no direct relationship between Island Number and the order in which the levels can / must be played, or the order in which the Islands become available in the [ MapWorldView ]

A level is playable if its depends requirements given in the island.xml, are met.
If a level has no "depends" attribute, it is always playable.

An Island button is enabled if the first level entry in the island.xml is playable.
NB: "First" means the first <level> tag found in the file.
In MapWorldView the game sets the enabled / disabled state of the corresponding button id="islandx" based on this.
A black arrow pointer is displayed next to an island button if the island contains a playable level that has not been completed.

Island.XML

Requirements: island.xml must have...
map must be a valid Map Level
icon must give a valid Image Resource ID from the global resources.xml
At least one <level> tag defining a valid level.

Map Levels

Requirements: For each <level> tag in island there must be…
button with id="lb_{levelid}" This is invisible until level is playable
SceneLayer with id="ocd_{levelid}" This is invisible until OCD achieved

Optional:For each level tag in island there can be one or more..
SceneLayer with id="levelpipe_{levelid}" This is invisible until level is playable.

What happens when levels become playable…

When you finish a level, this may make 1 (or more) other levels playable. When this happens the game will display the unlockfuse particle effect which moves from the completed level button, to the newly playable button. When the effect reaches the target button, that button becomes visible, as do any levelpipe_ scenelayers for that level.
If a level depends on more than one level, the unlock particles travel from each depends level only when the final dependant level is completed.

How a Chapter Ends

When the 'last' level in a chapter is completed, the player is returned to the MapWorldView screen rather than island.
NB: Last means simple the last <level> tag appearing in the island.xml. This need not be the last playable level, based on depends, but normally it should be.

Special Islands

Island4 has one special thing.. the signposts. Any signpost, in any level, launched from island4 will display the green terminal sign, rather than the normal wooden one. This appears to be hard-coded into the game.

Island1 should also be considered as special and treated with care. Not because of there’s anything hard-coded in the game for it, but because this is the island that GooTool places custom levels into. Guidelines for redesign of island1

Commands and Actions that can be used in island maps

Action: wogcorp_from_island, zoomout, pl_{levelname}, pm_{moviename}
Display: ss_{levelname}, hs_{levelname}
For more details see [ Commands and Actions ]