I couldn't resist and got started before I saw your last post. I just love Photoshopping maps, I guess.
I've made sea/land, experimented with roads, then realized that before I could go much farther some critical decisions have to be made. The first is where the "destination cities" should be placed. So I'm posting the draft map below as a basis for discussion about these critical placement issues. With destination cities the idea is to maximize as per three goals:
1) Make maximal use of historically important cities.
2) Spread the destinations out as much as possible so as much of the map as possible becomes relevant.
3) Avoid allowing any two destinations to be connected by owning just two roads.
And a fourth, perhaps... include London because it's now so famous and so that there's no reason to totally avoid Britain in the map.
Now those goals can be cross-contradictory. For instance, several cities in Italy were very important at the time but they are too close to Rome to include for game purposes. And it would be wonderful to include Alexandria or Memphis but if you do it's impossible to find a good destination between there and Byzantium, and Damascus was also very important. (I've made these city circles with red so they'd show up better here. Don't worry. They'll look like Trubetskoy's later.)
Sea routes are next: I've included what I think satisfy two goals: historical importance and frequency of use, and gameplay utility. Now if we can't get XML to support seasonal use only (and perhaps even if we can) an important question is should there be reset-to-three (or some such) terts in between ports so voyages are more costly? How many? Where? The Brundisium-to-Corinthus crossing should be less costly than the Roma-to-Carthago Nova one. And should stretches of sea routes be ownable terts that count toward your tert count and thus affect troop awards? It wouldn't be historically inaccurate to allow players to own sea routes since there were plenty of pirates around at the time and using your navy to limit their areas of control was important. And that said, wouldn't it be rather cool if we could find some way to make pirates randomly appear and take control of sea routes? I doubt there's a way for XML to support that.
I've used black lines to indicate sea routes to be added but Trubetskoy already has five on his map and we have to decide how to deal with them. He uses connected circles for the English Channel, the Straits of Gibraltar, and the Straits of Messina, and he simply has roads crossing water twice over the Dardanelles and the Bosporus. I can understand why his did those last two since they'd be the easiest of the crossings. So was the Straits of Messina. But the English Channel and the Strait of Gibraltar were rather treacherous. Just ask Julius about the Channel. Should we make all these free crossings? Some of them? Since we'll not have all those little circles if the Straits of Messina were to be free I'd just have the green and yellow roads connect. No special iconography.
Another issue: the Via Numidia (green road in North Africa) forks. The extra spur would be irrelevant to gameplay and could cause player confusion. As it is, this road serves only as an out-of-the-way tert someone could capture. It doesn't connect two different roads. Can I eliminate one of the forks?
Another: Trubetskoy did not name that little gray road that connects Massalia to the rest of the world in southern Gaul. On this map
https://sashamaps.net/images/gaul_vthick_140-2.png he shows it as just another station on a coast road but we need it to have that gray spur for gameplay purposes (otherwise it's just two from Rome and Lugdunum) and in any case we're basing our map on the one of his, not some combination of maps. And on this map
http://www.athenapub.com/aria1/_Eur/md_gaul-map-rhonemouth2.jpg it's indeed shown as on a spur. I've tried like heck to find a map where it's named but cannot. Would it be okay if I gave it a color and named it "Via Massalia"?
Finally: What to do about Sardinia? I'll show every other road Trubetskoy has shown (except possibly the "Via Futura" bits he's shown with dotted lines) but Sardinia was not very important and creating a sea route just so someone can claim one extra tert would clutter up the sea for no important reason. Theoretically it could be a way station between Ostia and Carthago Nova but that wouldn't be very accurate. When the Romans made that voyage if they stopped anywhere it was usually at Masalia because they liked to hug the coastlines. So would it be okay if I just ignore that little bit of road and make Sardinia a simple white blob like Corsica and Cyprus?
That's a boatload of questions and decisions to be made. It's going to take me a while to get all the roads done and while I'm slaving away at them we could be working on all these other matters. So please go through this long post carefully and repeatedly and supply as much input as you can. And it sure would be great if some other CCer's chimed in. There have got to be some folks here who know a lot more Roman history than I do.
Sardina. My original intent was to ignore it as it was not connected. Now that we have see routes, maybe we could connect it. 
