MicroStation and AutoCAD use 2D and 3D Cartesian coordinate systems that locate data at fixed coordinates. CAD coordinates are not inherently geographic locations; rather, they are locations relative to a simple geometric origin (0,0,0). To accurately position CAD data or any data in ArcGIS, you need to define the meaning of the coordinates used in the data. This is accomplished by defining a supported Esri coordinate system. .
MicroStation and AutoCAD use 2D and 3D Cartesian coordinate systems that locate data at fixed coordinates. The x-, y-, and z-coordinates are not inherently geographic locations; they are locations relative to an arbitrary geometric origin (0,0,0). The x-axis can be thought of as an easting direction and the y-axis as a northing direction, but they do not necessarily translate to grid directions in your spatial data.
Although you can create CAD data that corresponds to the x,y coordinates of a projected grid zone, without a supported means to identify which supported Esri coordinate system was used, the data is unlikely to be positioned correctly.
You can inspect and validate the completeness of a CAD file's coordinate system information using the file properties context menu option available when browsing for CAD files in the catalog pane.
Linear units in a CAD file are not dependent on, and they are not defined by, the data's coordinate system. They are a matter of the author deciding what the drawing units represent before creating the data.
As a general rule, all CAD drawings (or models) are drawn at full scale (1:1). One drawing unit can represent any linear unit of measure, such as inches, millimeters, meters, or feet. The decision is typically based on the level of detail the drawing is intended to capture. For example, the units in a drawing of the interior space of a building are likely to be in inches or millimeters, whereas a drawing of a survey plat or a landscape plan is likely to be in feet or meters.
ArcGIS Pro coordinate systems support coordinates in feet or meters. CAD drawings drawn in other units, such as inches or milliliters (sometimes used in architectural applications), must be scaled by georeferencing tools to properly position the data.
CAD data coordinate system (PRJ files)
By default, AutoCAD or MicroStation files do not contain Esri coordinate system information to define a coordinate system. The Esri undefined coordinate system is assumed when no coordinate system definition is detected by ArcGIS Pro for a CAD feature dataset (CAD file). When data is added to a map or scene in ArcGIS Pro with an undefined coordinate system, the coordinates of the data is assumed to be the same coordinate system of the current map or scene's coordinate system, which may or may not be correct. It is recommended that you define a coordinate system for all data added to ArcGIS Pro so that it can be properly positioned.
Coordinate system for AutoCAD files
An AutoCAD file may contain Autodesk coordinates system definitions from AutoCAD, AutoCAD Map, or Civil 3D, but currently ArcGIS Pro does not recognize these coordinate system definitions. However, an AutoCAD file may contain coordinate system information in the DWG or DXF. file created by the Esri ArcGIS for AutoCAD plug-in application, or as a result of the ArcGIS Desktop Export To CAD geoprocessing tool.
You can associate an Esri coordinate system to any CAD file by including a valid Esri .prj file containing the coordinate system information in the same file folder as the CAD file where the name of the file is the same as the CAD file, but with a .prj extension.
ArcGIS Pro does not recognize the Autodesk coordinate system information of AutoCAD Map 3D or Civil 3D.
Coordinate system for MicroStation files
You can associate an Esri coordinate system to any CAD file, including MicroStation files, by including a valid Esri .prj file in the same file folder as the CAD file. The included .prj file must have the same name as the CAD file, but with a .prj extension. MicroStation files may contain Bentley coordinate system definitions, but ArcGIS Pro does not currently use that coordinate system information and you must therefore define an Esri coordinate system definition using a PRJ file.
Universal CAD and BIM coordinate system (ESRI_CAD.prj)
To define the same coordinate system for every CAD or BIM file in a file folder, you can rename the .prj file containing the desired coordinate system to ESRI_CAD.prj. Then every CAD or BIM file that does not have a defined coordinate system will use the ESRI_CAD.prj file as its coordinate system. This is useful when all of the files in the folder should use the same coordinate system.
CAD data spatial transformation WLD and WLD3 files
When the coordinates in a CAD file do not correspond to the included coordinate system due to error or because the CAD file was drawn relative to an unknown position, you can specify a coordinate transformation using an Esri world file. A world file is an ASCII format file with two or three sets of coordinates that define a two point or three point, respectively, linear affine transformation to move scale and rotate the CAD data from where it was drawn to the proper coordinates of the included coordinate system PRJ file.
You can define a coordinate transformation for a CAD or BIM file by including a valid Esri WLD or WLD3 file in the same file folder as the CAD or BIM file. The included world file must have the same name as the CAD or BIM file, but with the .wld or .wld3 file extension.
CAD files must have a valid Esri coordinate system (.prj) before a world file is created since the offset values of the world file must correspond to a specific coordinates system as defined in the PRJ file.
A world file contains two sets of from-points and to-points to adequately define a transformation that moves, scales and rotates the coordinates of the file.
A WLD3 file is generated as the result of the CAD or BIM georeferencing tools.
Universal CAD/BIM coordinate transformation (ESRI_CAD.wld and ESRI_CAD.wld3)
To define the same coordinate transformation for every CAD or BIM file in a file folder, rename the .wld or .wld3 file containing the desired coordinate transformation to ESRI_CAD.wld or ESRI_CAD.wld3, respectively. Then ArcGIS Pro will apply that coordinate transformation to every CAD or BIM file in that file folder. This is useful when all the drawings are accurate one to another and all need to be adjusted in the same way.