Organizations often rely heavily on CAD files to display and manage their utility network systems. This reliance typically stems from a lack of staff or resources to maintain the data in a Geographic Information System (GIS). However, by migrating CAD data into a GIS environment, water utilities, local governments, and campuses can leverage powerful geospatial tools like ArcGIS Pro and ArcGIS Online to update and maintain their networks more efficiently.
Here are some tips and tricks for converting CAD utility data into GIS.
Differences between CAD and GIS
Before converting, it's important to understand the key differences between CAD and GIS. CAD files are organized into layers and can have point, polyline, and polygon feature types stored in one layer. In GIS, these three different feature types must be separated into different feature classes. In addition, GIS files require coordinate systems to align them to their location on the earth’s surface, but CAD files do not.
This is a screenshot of CAD data opened in ArcGIS Pro. Notice that the “V-Util-NGas” layer is shown in GIS twice: in the point group and the polyline group. When this one CAD layer is converted, it will have two feature classes in GIS.
Opening CAD Data in ArcGIS Pro
When you open the Catalog view in ArcGIS Pro, every CAD file will have the same five layers: Annotation, MultiPatch, Point, Polygon, and Polyline. Your CAD file may have additional layers; however, these are the only five layers you will need to use for the conversion process. Any additional layers that appear will have duplicate information.
Pro Tip: Request the CAD file owner provides a file containing only the data that needs converting, rather than an entire CAD file with several unnecessary layers.
Pro Tip: At the time of conversion, the Arc GIS software will expect a coordinate system/projection to be defined. Always ask the CAD file owner for the projection information of the CAD file. If the projection is unknown, consider trying the State Plane zone of the target site. State Plane is common among engineers because it minimizes distortion.
Conversion Process
Below are two methods for converting data from CAD to GIS. The first method shows the step-by-step process that is useful when you have a CAD file and are unsure of the correct coordinate system, you are not familiar with the contents of the CAD file, or if you need to convert only a few select layers. The second method shows the tool that can do it all in one step! This will convert your entire CAD file into GIS – but you need to be sure of the coordinate system or your feature classes could end up in the wrong state!
Conversion Method 1: Step-by-Step Process
Step 1: Add CAD Data to ArcGIS Pro
Open the catalog and navigate to the CAD file location. Add the Annotation, Point, Polyline, Polygon, and MultiPatch layers to your map. You will see a group appear for each feature type in the contents pane. When you expand a group, for example, the point group, you will have a layer appear that combines all the point features, and a layer from each CAD layer that contains point features.
Pro Tip: You can skip MultiPatch if you are not working with 3D data.
Step 2: Define Projection Tool
You can check if your CAD file has a projection by right-clicking on a layer in the Contents > Properties > Source > Spatial Reference. Here you will see the coordinate system details or “Unknown Coordinate System.” Use the Define Projection tool to assign a projection to a CAD with an unknown coordinate system.
Pro Tip: After running the tool, a .PRJ file will appear in your file explorer that will tell GIS what coordinate system the CAD file uses if you open it in another project.
Pro Tip: Define Projection differs from the Project tool; here we are giving a projection to a CAD file that does not have one yet. Project takes a feature class that already has a projection and creates a new feature class with the new projection.
Step 3: Convert Layers to Feature Classes
Run the Feature Class to Geodatabase tool to batch convert Annotations, Points, Polylines, Polygons, and MultiPatch layers into feature classes in a geodatabase. Here you will want to grab the first layer that appears when you expand a group. It should say “-Point” at the end of the name. This will allow you to convert everything at once, rather than converting several individual layers.
On the other hand, if you only need to convert a few layers from the CAD file, you could find those in the Contents Pane > Right Click > Data > Export Features. Then, bam! You’ve converted your data to GIS format. If not, continue with the next step.
Pro Tip: You may have to turn on the labels for your annotation class to see the annotations. If your annotation layer is hard to read in GIS, you may want to create new labels from points/polylines/etc. instead.
Step 4: Split by Attributes
Run the Split by Attributes tool on each feature class, using the “LAYER” field as the split field.
Step 5: Edit and Symbolize Data
Customize the data’s appearance and functionality to meet your project’s needs.
Conversion Method 2: The CAD to GDB Tool
The CAD to GDB tool runs the whole process described above in one step. It also will eliminate feature types if your CAD file does not use them. For example, if there are no MultiPatch features in CAD, they will not appear in GIS. This method also creates a Feature Dataset within your geodatabase for this converted CAD data to reside. Feature datasets function like folders within your geodatabase, where each feature class within the feature dataset has the same coordinate system.
Conclusion
Migrating utility CAD data into GIS might seem daunting, but with the right tools and techniques, you can transform your data into a more functional and manageable format. By following the steps outlined above, you’ll be well on your way to leveraging the full power of GIS for your utility networks.
Whether you need help with a single CAD file, or automating a large batch, feel free to contact us for assistance.