The map border is just an entity like everything else. You can more or less do what you want.

When talking about the map border though, it is important to remember that there are two of them, the "technical" map border which consists of 4 lines on the MAP BORDER layer, and defines the actual size of the map and the stopping point for things like drawing tools. Then you have the visual/graphical map border, which is just decoration.

For decorative map borders, you can create as many as you want, and shape them as you want. But the drawing can only have 1 technical map border (the 4 lines around the outside of the map), and that one needs to be rectangular, no weird shapes. Now, you don't technically need a technical map border at all, but without one, you're drawing tools don't have a border to snap to, and you can't use the resize drawing area command. Also, exporting and printing to map border won't work, you will always have to define areas yourself, but technically, these are just conveniences, not requirements.

Just one addition to Sue's explanation above.

From the small screen shot, it looks to me that this may be an FT export? If so, it may be a multipoly (depending on your export options). If it is a multipoly, it needs to be exploded |CC2EXPLODE| first.

(Note that exploding it will also means that any "holes" [lakes] in the landmass will disappear since they will be turned into their own polys instead of defining holes in the multipoly)

Looking at your screenshots, it looks like the white gap is part of the image. CC3+ doesn't add or remove anything from the image (shouldn't anyway, and I've been unable to get it to). So my recommendation is to have a closer look at the source image, seems there is a border on the bottom and right sides.

There is a setting called 'outlined' on the settings for the fill in the fill dialog, you can check that it is disabled, but I don't think that's what you are seeing here.

Technically, you can just chuck any template into @Templates\Cities\Floorplans to use that style. Note that it does look for certain tools to set the fill/sheet/other properties of the walls/floors it draws as part of the floorplan (The Wall, Default and Floor, Default tools), so if those tools aren't present, they will just use a solid fill instead, but the shape will be drawn, so you can just use change properties

I think you need to brush up on your conversions. 30 km is about 100,000 feet. Of course, you wrote 30k kilometers, which is 30,000 km or 100 million feet.