Reddit mentions of One Hundred and One Track Plans for Model Railroaders (Model Railroad Handbook, No. 3)

The best answer I can give you is to look at 101 Track Plans for ideas. While most of the layouts featured are based around HO scale, a 4' x 8' HO layout fits fairly comfortably in a 3' x 5' area in N scale, and with a few changes, can often be made to fit a 2' x 4' area.

In a small space, you have to be selective about what you put in. It will likely mean tight turns, so running big steam locomotives and the larger diesels are probably out of the question. Passenger cars and long freight cars are going to look funny on tight curves, and some may not run well at all.

Other ideas for you:

• Mike's Small Trackplans
  
• Carendt.com micro & small layouts

I would highly highly highly recommend picking up the book ["101 Track Plans for Model Railroaders."] (https://www.amazon.com/Hundred-Track-Railroaders-Railroad-Handbook/dp/0890245126/ref=sr_1_1?ie=UTF8&qid=1503265427&sr=8-1&keywords=101+track+plans) There is essentially a whole chapter dedicated to 4x6 sized layouts, as well as 4x8s, and it is a resource that will pay dividends if future space opens up as well.

It's a great idea book, and with only so much space to work with, a lot of interesting designs have already been created for that space.

Another resource you might consider, especially since you already are using Atlas track, is any of the Atlas HO track planning books. They may not have as much variety as 101 Track Plans, but some of them show you how to build a complete railroad from start to finish, which could be useful.

Hope this helps!

Not that I know of. I use SCARM, which is free, and it's worked pretty well aside from a bit of a learning curve. I hear a lot of people use Anyrail but I like free :)

I also highly recommend the 101 Track Plans book.