Creating a Synthetic Natural Environment

From X-Plane version 8.0 until at least version 8.15, the World Editor, included with X-Plane, cannot edit the synthetic natural environment.

The single best Web resource for X-Plane scenery editing is XSquawkBox. I am not going to go into any detail because it's already there. I will add a few pointers below.

Object Creation

Fortunately there is a really good open-source 3D modeling tool called Blender. It can be downloaded for free. Beware that there is a rather steep learning curve on Blender, but it is an industrial-strength modeling tool. You will need a plugin for Blender to read and save in X-Plane format, which can be found here along with a very good tutorial.

Object Placement

Since X-Plane version 8.0, there is no "official" method to place objects. A workaround exists, but it's not easy. Scenery objects are stored in a .DSF file, which is an unreadable binary format. A tool called DSF2Text, which can be downloaded from XSquawkBox, is used to "decompile" the binary .DSF into a huge text file (up to 60Mb). Then edit the text file, re-compile the binary file, and start X-Plane to see how it looks. There are more detailed instructions on the XSquawkBox Web site. You may have to download a new text editor to handle the large text file. I used GVIM which is extremely powerful, but not so easy to learn.

Scenery Visibility

Use X-Plane version 8.10 or higher if you are doing custom scenery. The user can control how many objects are shown with a setting in Settings->Rendering Options, which allows the user to sacrifice visual interest for higher frame rates. Unfortunately, unless the "Number of Objects" is set to "Totally Insane", X-Plane may choose not to render your new objects. Version 8.10 introduced a critical new feature that enables the scenery author to force it to render certain objects. This is described in detail at XSquawkBox. The default object set seems to randomly place skyscrapers throughout urban and suburban areas, producing a scene that is only appropriate for lower Manhattan or the downtown Chicago.

Scenery Data

Two excellent free resources are available. Google Maps has high-resolution satellite imagery available for most urban areas in the US, and lower resolution imagery everywhere else. The interface makes it very easy to scroll around a wide area and see where things are, and you can toggle back and forth from an image to a map to identify roads. Terraserver USA has higher resolution full color urban imagery, but with a more annoying interface. Choose "Urban Areas" (if available) for the best imagery. Click the "Info" link to get latitude and longitude coordinates for the image (necessary for editing the .DSF file). Click the "Download" link to get a contiguous image that you can save and possibly use as a texture.

Roads

Having some more streets and roads visible will help you navigate in the air, and make it easier to place objects. Under Settings->Rendering Options set "Number of Roads" to "Tons."