Defining a coordinate system for a CAD dataset

When you define a coordinate system for a CAD dataset, the CAD format determines how the coordinate system is stored.

CAD format	Coordinate system
AutoCAD DWG	Embedded in the CAD file
MicroStation DGN	Stored in an external <filename>.prj file with the same name and in the same folder

ArcGIS honors a companion (.prj) projection file for both AutoCAD and MicroStation formats. An external .prj file takes precedence over an embedded coordinate system when both spatial references exist. A projection file must not contain spaces; rename the CAD file if necessary. The .prj file is a hidden file and not viewable in the Catalog window.

A universal projection file applies the same coordinate system to all CAD files in the same folder. You can save a .prj file as a universal projection file using the reserved name esri_cad. The esri_cad.prj file is applied only to CAD drawings in the folder that do not have a coordinate system already defined.

Steps:

1. In ArcCatalog or the Catalog window, right-click the CAD dataset and click Properties.

   This opens the CAD Feature Dataset Properties dialog box.

2. Click the General tab.
3. Click Edit.
   This opens the Spatial Reference Properties dialog box.
4. Click one of the following:

   Select	Opens the Browse for Coordinate System dialog box. Browse the coordinate system folders, click a predefined coordinate system, and click Add.
   Import	Opens the Browse for Dataset dialog box. Navigate to an existing dataset you want to copy, click the dataset, and click Add.
   New	Opens a dialog box that allows you to define your own projected or geographic coordinate system.
   Modify	Opens a dialog box that allows you to customize the current coordinate system.
   Clear	Sets the coordinate system to Unknown.
   Save As	Saves the coordinate system to an alternate (.prj) projection file. Use this option to create a universal esri_cad.prj file.

5. Click OK on the Spatial Reference Properties dialog box.
6. Click OK on the CAD Feature Dataset Properties dialog box.

Note:

The Export To CAD tool automatically exports the coordinate system to DWG formats (version 2007 or higher).