Understand the World and User Coordinate Systems

There are two coordinate systems: a fixed system called the world coordinate system (WCS) and a movable system called the user coordinate system (UCS). By default, these two systems are coincident in a new drawing.

Normally in 2D views, the WCS X axis is horizontal and the Y axis is vertical. The WCS origin is where the X and Y axes intersect (0,0). All objects in a drawing file are defined by their WCS coordinates. However, it is usually more convenient to create and edit objects based on the movable UCS.

Work with the User Coordinate System

Virtually all coordinate entry as well as many other tools and operations reference the current UCS. 2D tools and operations that depend on the location and orientation of the UCS include the following:

• Absolute and relative coordinate entry
• Absolute reference angles
• Definition of horizontal and vertical for Ortho mode, polar tracking, object snap tracking, grid display, and grid snap
• Orientation of horizontal and vertical dimensions
• Orientation of text objects
• View rotation using the PLAN command

Moving or rotating the UCS can make it easier to work on particular areas of a drawing.

You can relocate the user coordinate system with methods such as the following:

• Move the UCS by defining a new origin point.
• Align the UCS with an existing object.
• Rotate the UCS by specifying a new origin point and a point on the new X axis.
• Rotate the current UCS a specified angle around the Z axis.
• Revert to the previous UCS.
• Restore the UCS to be coincident with the WCS.

Each of these methods have a corresponding option in the UCS command. Once you have defined a UCS, you can name it and then restore it when you need to use it again.