IMPORTANT: This is a new worldspace and should be at the bottom of your load order. 

Thanks to Comrade365 for discovering the bug and fix.

NEW WITH 0.2.000: Supply lines and moving settlers should work, and Settlement Management Software should recognize it.  Earlier saves may not be correctable because of quest trigger fixes.

This is originally intended as a test cell, I don't suggest using it as a "real" settlement yet but welcome testing.

WARNING: Save before using this.  I'm not sure what happens if you uninstall after using this because it adds a Settlement.  Removing the plugin may screw up internal settlement data somehow.

What is this?
I was frustrated trying to learn building with the Workshop pieces, not having a nice large flat area to experiment in.  

I couldn't find a mod anywhere that did this, so I decided to make a test cell, with completely flat land, and nothing in it but the workbench.

Why not just use the Boston Airport?

Boston Airport's only available if you join the Brotherhood of Steel, and (I think) after the Prydwen arrives.  I wanted something that would work fairly early on in the game.

Can I treat this as a regular settlement (with supply lines, send settlers there, etc.)?

You can try if you wish, but I have not tested this at all yet.  For now, I don't suggest you rely on this as a "real" settlement, it's meant only as a way to play with the workshop pieces in a nice flat area.  If you do have success with this, or problems, please let me know.

How do I get there?

As of 0.1.0002, there is a manhole near the Sanctuary Hills sign by the bridge.  That brings you right to the new worldspace workshop, and a manhole there brings you back.   As of 0.2.000 settlers may use this door, and supply lines/moving settlers there should work.  I'm not 100% sure about moving settlers from the new worldspace back out, however.

You may also the debug console:

coc XhirisSandboxOrigin

What about XBox and Playstation?

Not yet.  I've added a "door" so you can get there without console, but I don't have XBox or PS3/4 so have no way to test this. I'm also not sure about any side effects of adding a new worldspace or a door to/from it in a settlement (see above).

If you know how to port this and are willing to try/test, please feel free.  I only ask you let me know how you did it.

Is this Lore Friendly?  Immersive?

Sorry MxR, this is just a test cell.  It might be fun to integrate this in a more immersive, lore-friendly way (say an abandoned construction site?), but really don't know how to do that.

Future Plans/Ideas

• Provide unlimited building components, by default.  
• Prevent taking those components out of the area, so this isn't considered a cheat (I don't care about cheating, but want to see if this is possible)
• Accessible by an item or holotape (especially if adding a door to the world causes problems or clobbers other mods)
• Add markers/rulers so you can gauge area
• Map? (it's just a flat square with nothing in it, but incorrectly shows the Commonwealth world map)
  

Referenced Tutorials

MANY thanks to these YouTubers for their Creation Kit tutorials:

A simply brilliant tutorial by markymint.  It covers all you need to create a new outdoor settlement in the Creation Kit in under 10 minutes.

• Creation Kit - Settlement Tutorial: Part 1 - The Basics (Fallout 4)  
  

These, by Rage Gamer on YouTube, helped with creating the world space and region bounds.  He also covers landscaping, weather, sounds and other aspects of external cells.  BEWARE, he swears up a storm during his epic battles with the Creation Kit (can't say I blame him, CK can be rather user-hostile)

• Fallout 4 Creation Kit Basics : Tutorial Episode 7 External World Spaces 
• Fallout 4 Creation Kit Basics : Tutorial Episode 9 External world spaces 2