Is there a way to bring in vectors from an AutoCAD file without them being filled? I come to Blender from the CAD world.  I am teaching Blender to 12 students.  We are working on a scene that happens in Charleston Harbor in 1862.  I found an old chart and scaled it to full size using AutoCAD.  Then I traced it making closed polylines.  I can bring it into Blender as an FBX, but those closed shapes come in looking like this image:


I want to make a landscape using the shapes I created, giving it height.  Do any of you know how I might un-fill the shapes?
There's a plug-in for importing DXF files that gives  you a lot more options than FBX and it looks like it imports linework as paths instead of meshes.