You'd need a bitmap image version (BMP, PNG or JPG) of the map you could import into the CC3+ drawing on one of the lower Sheets, and then resize it to fit the size of map you're intending to draw, but yes, this is eminently practical.

To import the bitmap, make a new Sheet and a new Layer both called BITMAP in the FCW file you'll be working with, and make sure both are checked to be the active Sheet and Layer.

Then to import the bitmap, use the drop-down "Draw" menu, and click on "Insert File". Navigate to wherever your file is stored, click on it and click OK.

You'll then have it on the cursor in your map. Click once to secure its top left corner, and then move the cursor to enlarge the bitmap to the size you need, and click again to finish the command.

You might find it helps to set up a snap grid of a size to be useful in finalising the bitmap size, and make use of that during the import process.

You can then check the image size is correct by using the CC3+ measuring tools against items of known sizes on the image. You can rescale the size of the drawing very precisely after import too, if necessary.

And if you get stuck, just ask again on the Forum!

One final thought. You might like to check around on the Forum for topics created by @mike robel who's done a lot of high-quality work of exactly the kind you're wanting to do, specifically to create board wargame maps using CC3+.

Though the "standardised" abbey plan only really works - if sometimes quite loosely - for medieval European monastic sites, notably those of the Cistercian and Benedictine orders.

Clearly a delightful spot; very tempting for a dragon...😉

If you have it, you might be interested in trying out the sketchy contour line symbols in the Black & White Towns CA issue from 2015, which are similar in appearance to those in your castle hill lines (though naturally, you'd need to add your own background colouring for those, as B&W only).

It does also depend what sort of effect you're looking for. If you want to make it look like a boundary line, for instance, you might try a polygon with an Edge Fade, Inner effect on its sheet, and adjust that till it looks right. Or you could try adding a Glow effect to the various symbols involved, if they're actually the key things (though it sounds more as if it's the whole region you're wanting to highlight).

Best advice would probably be to keep experimenting and thinking about what you'd prefer to see; playing around with the options in the CC3+ effects is never time wasted, even if you can't get quite to where you'd originally thought you might!

Or maybe even swapping out the dark lettering for a much paler colour, and adding a darker outer glow to it, as that sometimes helps. Getting text right is always tricky though.