The strange band across the map you describe may be down to the number of passes the render has to do to export the bitmap.

Use the command EXPORTSETMPPP to find out how big each pass is. The default value is 4000000 (4 million). If yours is still at the default, change that to 40000000 (40 million) and try the export again.

Well... you could move the "lights end" sheet up the list till the buildings are above the light effects altogether.

Then, given that they are now far too light and need to have that light dropped to 50% like the lit part of the map, you could add an RGB Matrix Process to each of the "Symbols Buildings" sheets, and set it up to give only half the unity colour. (Unity is a diagonal of ones)

Notice how I also moved the SYMBOLS Trees sheet up the list to keep it above the Lights - End sheet. That's because I'm not sure if an RGB Matrix Process will work on regular symbols (ie, not shaded symbols like houses and buildings)

You would need to put the blur after the cutout.

You can make separate symbol catalogues from the same folder if you haven't split them into subfolders.

Check out page 90 in the Tome for the basics.

If you get stuck, just shout.

You can do it using GIMP.

When you get to the point in the video half way through, you don't need to go any further saving it as a pattern in GIMP. Just export yourself a png file to your User folder.

It works better on some images than others. Try not to pick images that are vastly different on either side or top and bottom.

If you can draw your own pattern you could use Krita (another free bitmap editor), which has a wrap feature to give you an endlessly repeating canvas to draw on. This video talks about saving a pattern within Krita, but he does say about 90 seconds in that you can just export it to png the moment you're happy with the drawing. (this video does go a long way off track the further through you go)