It is hypothetically possible to draw a vector drawing in inkscape, export them as a dxf file, load them in AutoCAD, turbocad, etc, export as a dwg, import into sketchup (dxf might go straight in as well, I can't remember), make a 3D model, load it in quark, export to map, import to constructor, export to dif, and load in Blockland.
In fact, you can take a sketch on paper, scan it, convert it to a vector format, and end up with a working map at the end of the day.