A quick tour of working with CAD data

What follows is a high-level overview of the tools and user interfaces available in ArcGIS for working with CAD data.

CAD data organization

Computer-aided design (CAD) data is a file-based data source. You can connect directly to CAD files on the fly and manage them as read-only datasets without using conversion tools.

CAD data is organized into a geodatabase-enforced schema comprising five generic feature classes: annotation, multipatch, point, polygon, and polyline. Alongside the generic feature classes, AutoCAD drawings (version 2007 or higher) may include subset feature classes that are uniquely named and contain entity-linked attributes.

When you add a CAD feature class to ArcMap, ArcScene, or ArcGlobe, all standard map functions are enabled, including attribute tables and labeling functions. You can snap to geometry, substitute symbology, and use it with all geoprocessing tools that accept feature classes or layers as input.

Coordinate systems and geographic transformations

You can define a coordinate system and a geographic transformation and create and edit metadata for CAD datasets. The information is stored in external support files and moves with the CAD dataset when it is managed in the Catalog window.

Defining a spatial reference

To define a coordinate system, right-click the CAD dataset in ArcCatalog or the Catalog window, click Properties to open the CAD Feature Dataset Properties dialog box, click the General tab, then click Edit.

AutoCAD drawings (version 2007 or higher) have the extended ability to store the coordinate system in the CAD file. In cases where both internal and external spatial references exist, the external projection file takes precedence over the embedded coordinate system.

The Georeferencing toolbar

You define a geographic transformation for a CAD dataset in ArcMap using the Georeferencing toolbar. To preserve the aspect ratio of the CAD dataset, only commands that perform two-point similarity transformations are enabled; all others are unavailable.

Universal projection and world files

Universal projection and world files enable you to apply a common spatial reference and a geographic transformation to all CAD files in the same folder. Both files use the reserved name esri_cad. ArcGIS applies the information only to CAD drawings that do not have a coordinate system or transformation already defined.

Adding CAD data to a map

You can add an entire CAD dataset or its individual feature classes separately. As CAD data is added, ArcMap automatically creates a group layer for each CAD dataset and enables additional property tabs for managing the display of the underlying data.

To Add CAD data, do the following:

• Drag CAD data from a Search window into ArcMap.

• Drag CAD data from a Catalog window into ArcMap.

• Click the Add Data button , navigate to your CAD data, then add it to ArcMap.

Rendering

When you add CAD data to your map, ArcGIS attempts to reproduce the original appearance of the source file by rendering default symbology. Properties such as font names, color, and line thickness are read directly from the CAD file. Proprietary and vector-based fonts that do not have an ArcGIS equivalent are substituted with the Arial font. Line symbols unique to AutoCAD or MicroStation are defined with the style file ESRI-CAD.style.

CAD properties and attribution

The attribute table for each CAD feature class is a virtual table that exposes property values for geometry, layers, text, and user-defined attributes contained in the CAD file. The field values can be queried, used as filtering criteria for visualization tasks, and computed as feature data.

Read-only CAD fields are used in the CAD feature class virtual tables. When you add CAD data to ArcMap, CAD property fields that are nonessential for rendering or query operations are turned off by default. You can turn them on using the Fields tab on the Layer Properties dialog box.

AutoCAD drawings

AutoCAD drawings can contain CAD-defined feature classes with entity-linked attributes.

Entity-linked attributes are viewable in the virtual attribute table alongside the CAD property fields. They are automatically imported to a geodatabase with the input features using any geoprocessing tool that accepts a feature class or layer as input.

Visualization

You can change the default CAD symbology without converting the CAD file to a geodatabase format. Use the Symbology tab in the Layer Properties dialog box to change linear and point features. Use the Fonts tab to change CAD annotation features.

You can restore the default CAD symbology in the Symbology tab. If you save the map, your changes are saved in the current map but do not affect the display of CAD symbology in other maps.

Definition queries

Query Builder accepts CAD property field values as input. You can use definition queries to filter out unwanted CAD geometry and display only the features you need to integrate with your map.

When working with AutoCAD drawings, an alternative to using definition queries is to create CAD-defined feature classes in the AutoCAD application using ArcGIS for AutoCAD.

Drawing layers

CAD drawing layers are layers contained in the source CAD drawing. When you add CAD data to ArcMap, the initial visibility settings are determined by the layer states that were defined by the CAD application at the time the CAD file was saved. You can override these visibility settings from the Drawing Layers tab in the Layer Properties dialog box.

Fonts

All text styles in a CAD annotation feature class are listed on the Fonts tab on the Layer Properties dialog box. Color, font, and formatting can be changed, but size cannot. To change the font size of CAD annotation, it must be converted to a geodatabase annotation class.

Importing CAD data to a geodatabase

Importing CAD data to a geodatabase gives you the ability to edit the information, perform cleanup operations, create topologies, and incorporate it with your existing GIS data.

CAD feature layers

To import CAD data in ArcMap, right-click the CAD feature layer in the table of contents and click Convert CAD Feature Layer from the shortcut menu.

Use the Copy_Features tool to import a CAD feature class or feature layer to a geodatabase feature class. This tool also accepts selections as input.

CAD feature datasets

To import an entire CAD drawing in ArcMap, right-click the CAD feature layer in the table of contents and click Convert CAD Feature Dataset from the shortcut menu.

Use the CAD To Geodatabase tool to bulk load entire CAD datasets to an existing geodatabase. This tool automates a series of conversion procedures that includes importing CAD annotation and merging identical feature class names, types, and attribution. The tool accepts multiple CAD files as input in mixed DWG and DGN formats.

CAD annotation layers

To import CAD annotation in ArcMap, right-click the CAD annotation layer in the table of contents and click Convert to Geodatabase Annotation from the shortcut menu.

Exporting geodatabase information to a CAD file

You can export feature classes, feature layers, or shapefiles to native AutoCAD or MicroStation CAD formats with the Export To CAD tool. The tool creates new CAD files or appends data to existing CAD files.

To export data from ArcMap, right-click the feature layer in the table of contents and click Data > Export to CAD from the shortcut menu.

Basic operation of the tool requires the input feature, output CAD format, and output path and file name. You can export data directly or combine the tool with other tools in a geoprocessing model or script to automate conversion tasks.

The type of data that is exported to a CAD drawing is determined by the destination CAD format and the limitations of its native CAD platform. By default, the Export To CAD tool creates a drawing layer for each input feature class or layer and generates the following entities or elements:

Input feature	Output to DWG and DXF	Output to DGN
Point	Point	Zero-length line
Line	LWPolyline, line, arc, circle, or ellipse	Complex chain, line, arc, or curve
Polygon	Closed LWPolyline	Complex shape
Annotation	Text	Text

Seed files

You can use a seed file to store layer names, styles, and other common settings. By default, the Export To CAD tool exports features to layers in the seed file that are named the same as the input feature layer name or feature class name, when they exist. You can also use seed files to store user-defined CAD objects such as AutoCAD block definitions and reference them individually during execution using reserved CAD fields.

Reserved CAD fields

Reserved CAD fields are used by the Export To CAD tool to override the tool's default behavior and generate specific CAD output. You can use them to create CAD data that conforms to specific standards.

You can add reserved CAD fields directly to a geodatabase feature attribute table or manage them separately in stand-alone tables and join them to existing tables. You can create them individually or add them in predefined groups using the Add CAD Fields tool.

AutoCAD drawings

By default, output to DWG formats (version 2007 or higher) includes CAD-defined feature class schemas and attributes attached to AutoCAD entities.

For each input feature class, the Export To CAD tool embeds a feature class definition in the AutoCAD drawing file, comprising the default AutoCAD entities that are generated for the feature. All feature attributes are exported as AutoCAD xrecords and linked to the appropriate entities. Similarly, the coordinate system is also exported and embedded in the DWG file.

For detailed information about how this data is structured, reference the ESRI document Mapping Specification for CAD available on the ArcGIS for AutoCAD Resource Center.