When setting up a complex mapping project, especially one that involves insets at different scales, I usually start with rectangular viewports. They regen quickly and are simple to draw.
When I am ready to finalize the layout for plotting, here’s one of those handy tools that used to be hidden as a command line only option, which is now available on the ribbon – Viewport Clip. It offers a quick and easy way to convert viewport shapes from rectangles, to any other closed shapes – polygons with more than four vertices, and even circles, ellipses or free-form spline curves.
The Clip tool is located on the Viewports panel of the ribbon View tab. This example shows the AutoCAD Map 3D ribbon, but it’s available in Civil 3D, and standard AutoCAD, as well.
Die-hard command line users can still enter the original VPCLIP command.
You can use this tool to convert a rectangular viewport to an existing object, (as long as it’s closed), or use option P to draw a new closed polygon on the fly.
Once a viewport has been clipped, you can use this same command, with option D to delete the clip, which restores it to the original rectangular shape.