Unreal World
Basic Information
It's 3D and Initially Solid
Everything in an Unreal game takes place within a large 3-dimensional space. The boundaries of this space can be seen in a 2D UnrealEd Viewport, by zooming out as far as posible with the mouse.
In a blank map, the world is completely solid. Mappers make spaces for rooms, corridors and outside areas by carving out parts of this solid space using Constructive Solid Geometry (CSG) (this is completely the opposite of most other 3D game engines, where the world is empty space which must be partitioned off to make play areas). These carved out spaces are then populated with actors (placeable objects representing weapons, lights, health, player spawn points and more). It is in this environment that the game takes place. Maps with outdoor settings appear to be within an enourmous space, with a sky and often distant terrain features. These are in fact part of an articificial projection, the SkyBox.
I think of the space in UED as a big box-shaped mountain. As a caveman, you will have to carve out your cave from this mountain, put your furniture in it and paint some walls. And when it's all done, you should have a nice place to live in, or play in.
What's different about your "cave" and the cavemans cave is that they never lived in caves and you will stay away from your, as you are so sick of knowing every way to go, every error you made and/or that you're tired of playing it because of the beta-testing.
- LegalAssassin
Tarquin: The above is more or less duplicated at CSG.
The Unreal Geometry and [Unreal Actors]? pages provide some more detailed information on how the geometry is actually handled within the Unreal Editor.
The Technicalities
Units
The size of the world is:
- 65536 = 2^16 Unreal Units in Unreal 1 and Unreal Tournament.
- 524288 =2^19 Unreal Units in UT2003 and Unreal 2
To find out how these units relate to the real world see: General Scale and Dimensions, UU
The Co-ordinate System
The Unreal engine uses a left-handed co-ordinate system (see 
Handedness for definition & pictures).
The Y axis is inverted compared to normal configuration used in maths or physics.
Imagine a plan view of the Unreal world. The X axis runs from negative to positive as you move from left to right. The Y axis moves from negative to positive as you move from top to bottom. The Z axis (that you can't see in a plan view) determines height. As you would expect the Z axis runs from negative to positive as you move upwards in the world (out of the screen on a plan view).
Other Stuff
Could mention actors and things like that I guess but putting it here simply duplicates heaps of stuff elsewhere. Makes me a little uneasy about it.
Discussion
(Entropic, commenting elsewhere) Even this page sucks for an introduction for new mappers
Tarquin: Yup. It is definitely work in progress. It was my intention here to explain the basic concept: that a map is a large abstract 3D space, which is solid at first, carved out with BSP, then populated with actors, into which the player is then dropped. (hey, that's not too bad! feel free to use for the intro!). It's also meant to be a place to find stuff like how co-ordinates work, and how big the world itself is. So it needs a nice, easy intro, and then clear headings for the more complex stuff.
Need to link Left-Handed Coordinate System
SuperApe: Should this be worked into other introductory pages? Which ones?
