To make it transportable (i.e., to fit in my car) I had to make this in three pieces.  Lay out the foam sheets and mark the plan on it with a Sharpie.

Note that the plan here is a topological map; you need to cut out the various levels.

Here the topological levels are cut out and crudely shaped.  Don't do the final shaping yet, at least on the lower levels -- you need to get the glue down.

Once dry, use a long sharp thin flexible knife to cut the topo map properly to shape.

This will take quite some time, and be kinda fussy, and make a mess.  Don't do it indoors.

I had already built the Front Gate of Erebor.  Here is testing for fit.  It is too heavy and too awkward to be permanently attached to the map; it must be transported separately.

Using a sharp utility knife with a snap-on blade, cut a trench in the foam for the river.  Using a sanding block, form the low-lying area a bit.  Using a heat gun, make some of the flat areas less flat.  Don't use the heat gun on the mountains, it magnifies the threshold between levels.  Be careful with the heat gun, and do this in good ventilation or not at all.

Image on the right shows the whole map (and the MDF cut to shape for the City of Dale, about which more later).  Image below shows a detail of the river and a couple of areas hit with the heat gun.

Now making the surface.  Using something like four tubes of caulk per map, goop it out, and spread it with your hand.  Takes some practice.  You want it to adhere completely, not be too thick, and you want to use the texture created with your hand -- don't try to smooth it too much.  If you wanted smooth, you didn't need to cover it with caulk.  At this point also hit any transitions between the levels of the mountain that you want to obscure or minimize.

Image left is partially done.  Image below is done.

You can throw some sand on the caulk while it is still wet, for texture.  Not too much.

After the caulk is dry (a day or two), spread some white glue (or caulk) and toss the sand there to create some scree slopes, and the creekbed.

In the image below you can see some of the scraps (cutoffs) from Stage 4.

Slap brown paint on the flat areas, and grey paint on the mountains.

This is intended to be a playable map, so distinguishing between the area that is sloped and that which is not is important.

Mix some dark brown, maybe with a touch of black, with a bunch of 70% rubbing alcohol in a cheap plastic squeeze bottle.  This gives you a runny wash.  Mix it as well as you may.

Then just squeeze out some of the wash here and there on the mountain, to run down the slope.  As shown.

Take a cheap disposable brush, a fairly big one (4 inches, maybe), and drybrush the whole thing with off white.

This step fixes a lot of errors on the map, and brings out the riverbed texture, and so on.

Take another cheap brush and some reduced white glue (maybe 2/3 glue, 1/3 water?), mix well, and then splotch the brush on the map where you want flock.  Leaving small parts unflocked looks better than trying to do a complete job -- the drybrushed brown showing through is actually good.  Do this together -- spread some glue, flock it, more glue, flock it.  The glue has to be wet when you flock it, so you can't glue up the whole thing and then flock it.

Having multiple different colors here is a good thing -- in the image to the right you can see some lighter patches, darker patch down where the marshy area is, and so on.

One detail I forgot to discuss above -- the Ruins of Dale.

So you see in the Stage 6 image that there was a piece of 1/8" MDF cut to be the base of the ruined city of Dale.  And then in later images you see Dale fully modeled.  The issue is this: really cool looking means unplayable.  To solve this problem the city of Dale is removable (the base is not glued down).  So it can look cool, but when troops move or fight across it, it can be removed for play.

The buildings and walls and ruins of dale are all made out of the same pink rigid foam as the maps.  Buildings are cut with a very sharp exacto knife, then just pieced together in any way that amused me.  Including smashing some of them while making Jolly Green Giant noises.

More ruined city of Dale.

Building it up with tiny buildings is tremendous fun, I gotta say.

Another view.

After you've got the buildings you want, and some gravel for rubble, slap the whole thing with black paint, then slap it again with gray paint, then drybrush off white.  Any pieces that get broken during the crude painting and drybrushing can just be touched up and glued back (or glued down as rubble).

This step was trivial in terms of total time involved, but has a massive positive impact in how cool the whole thing looks set up on display.

I cut three stylized background pieces out of pink sheet insulation and painted them as a cartoon/stylized mountain rising behind the Erebor Gate.

It took three colors of paint (grey-blue, white, and halfway between the two) and maybe two hours of work including cutting it out and painting it.

The pieces are glued to thin wooden slats to allow them to be slid underneath the mapboard.  This allows them to be removed to actually play the game, as otherwise the Human/Dwarven/Elven side cannot easily reach their stands to move them.