00:01This video is the first in a four-part series...

00:02...that shows you how to overlay CAD data in a map document.

00:06This one covers step one, defining a spatial reference.

00:12CAD drawings don’t natively support the ArcGIS projection system...

00:15...so it’s important to define one before adding it to a map document.

00:20A spatial reference defines the coordinate system from which the data will be projected.

00:24Without one, ArcGIS cannot project the dataset to the coordinate system in your data frame.

00:30It also uses the linear units to calculate areas and distances.

00:34This is critically important if you plan to use the data with geoprocessing tools...

00:38...to perform analysis, or load the data into a geodatabase.

00:43When you define a spatial reference...

00:45...the coordinate system is stored in an auxiliary projection file...

00:48...unless it is an AutoCAD format 2007 or higher...

00:52...in which case it is embedded in the actual source file.

00:56It is also important to note that defining a spatial reference does not modify the geometry...

01:01...nor does it georeference the dataset.

01:04Georeferencing is a separate task...

01:05...that you perform in ArcMap with the georeferencing toolbar.

01:11To define a spatial reference...

01:13... right-click the dataset in the Catalog window and choose Properties.

01:17The General tab displays detailed information about the spatial reference.

01:22In this case, because I haven’t defined one yet, it reports an unknown coordinate system.

01:26To define one, click the Edit button and open the Spatial Reference Properties dialog box.

01:31CAD data is typically drawn flat to a local coordinate system...

01:34...so choose a projected coordinate system...

01:36...that will produce the least ground-to-grid scaling discrepancies.

01:40If you're unsure of the name, you can type a keyword and generate a list.

01:44For this example I’m going to import one from an existing dataset.

01:49...so I browse to the dataset, select it, and then click Add...

01:54...and then click OK to apply it to the dataset.

01:57Once you define a spatial reference, all of the feature classes contained in the dataset...

02:01...will reference it when you add them to your map.

02:06The next step in the workflow is to add the CAD dataset to your map document.