I just reviewed a bunch of mapping software see
http://eveslist.crisses.org/Resources/Mapping I'm not finished with going through the list, and I'm on a Mac -- but so far the cheapest/easiest solution I have for desktop is Dia (open source, basically a "visio" knockoff) and creating custom "shapes". I made about 8 shapes (top-down architectural style: doorways, trees, helipad, stairs, etc.) and drew a preliminary map. It came out alright. I'm a graphic designer (and programmer, and...) -- so I'm up for creating a whole "shape set" for creating shadowrunning maps in Dia (over time -- now that I have the "hang" of making Dia shape sets).
Application:
http://sourceforge.net/projects/dia-installer/It's at Sourceforge, there's Windows & Mac ports of Dia. Creating shapes -> you can make svg files in Illustrator/Inkscape and import them, or you can actually use Dia itself. Warning: there's no "rotate" in Dia currently. They're working on it. So when I export a shape where horizontal vs. vertical matters, I have to rotate it and export it again in another program. ick.

Such is the world of open source.
I don't have my shapes online yet, but this shape set is already available and could be helpful for creating maps:
http://dia-installer.de/shapes/building_site/index.htmlrequires installation after installing your Dia installation.
If you liked old-style SR1/2/3 node maps, you can use Dia to make networking diagrams

(It's a standard shape set, no extra install required.) Remember: a wired network is a safer network. All the corps will only have wireless at specific points -- datastores and goodies will quite probably be "hard wired" to avoid being hacked, so I don't see why the old-style node maps/network diagrams went "out of style" -- they still are valid (just make a few items wired AND wireless (i.e. hubs/routers/access ports) while others are completely wireless and others are completely wired). This is EXACTLY the type of use Dia is made for, so I'd say go to town... I'll have to draw an example SR4 network map soon, just so people can see Dia at work...