A lot of this information is the same as Locations. Rather than repeat it here and bore you, just read the Location Properties section if you have not yet. Only new information will be covered.

The Exits field displays the exit data assigned to the current Overworld.
The Unk. Palette indicates an unknown purpose palette assigned to the current Overworld.

The L1/2 TS fields indicate which tilesets are in use by the current Overworld. Unlike Locations, each packet of tiles is individually assigned.

Sprites 0 - 3 indicate which sprites can be used by the events packet (eg: Ferry).

This window will display the current tileset used by the loaded Overworld. From here you can choose one or multiple tiles to place and create your overworld.

The upper half of the swatch is Layer 1 and the lower half is Layer 2. The overworld is different than the locations in that you must disable layer 1 in order to place layer 2 tiles. Attempting to place a layer 2 tile with layer 1 activated will place a layer 1 tile.

This window shows the various overworld exit data for the current overworld. An overworld exit is a point on the map that your characters can step onto, and enter a chosen area.

Two major differences here.
Name - the string displayed in-game when the exit is stepped upon
Available - The default availability of the currently selected exit (not all exits are visible from the start).

The exits will appear in the overworld window as red empty squares. Using the overworld exit properties window, you can manipulate these exits, move them, delete them, add more of them, make them take your characters to any location you wish, etc.

Note: Exits can only appear in-game on certain tiles. At this time, Temporal Flux cannot edit this.

Works the same as in Locations.

The file to the left was created and automatically named ctow000.png.

In this example, I have scaled down the picture quite a bit. The original file was 506k in size, and 15356 pixels wide by 1024 pixels high.