Taking an initial look at the in game map for Tamriel, there are some glaring issues. For one, just taking a look at the placement of Pact zones with the Rift connecting to Stonefalls, the mountains that are meant to separate Skyrim and Morrowind are all but gone. The swath of land known as the Velothi mountains, which also contain the city of Blacklight do not have room to exist on our current map. In fact, the size of this land is about the same as Glenumbra.
Now, I get that there are creative directions that ZOS can take with the game. But eliminating pieces of land should not be one of them. While I'd not be surprised to hear the lore excuse that "Maps are not always drawn correctly," the extent to which some areas of the Map of Tamriel are incorrect go so far as to eliminate entire locations from Tamriel. So, I thought I'd prepare an (amateur's) map of Tamriel, annotated with the issues that are most obvious. (Note, the original outline was traced off of:
This map of Tamriel, which has remained consistent for a very long time)

The map shows the majority of the issues with the map, and to some extent how to fix them, but some things are better explained here.
Click on a zone and look at its internal map. This is the map that has the most accurate borders, as it contains the extent of the playable area. Some zones, like Craglorn, also contain a large portion of unplayable areas upon their maps, such as mountains. Let's look at Craglorn further. If you click within the zone, you'd notice that it looks a bit like an oval- fatter towards the middle and tapering off towards the Cyrodiil border. If you click out of the zone and look at it from the Tamriel Map side, it is no longer shown to taper into cyrodiil, but share a substantial border as well.
A main feature used by ZOS to make zones flow together a bit better is to adjust the scaling of the borders. In many cases, this helps the aesthetic appeal of the map's boundaries. Here, take a look at a map of our in game zones if the borders did not meld together:
at Tamriel Foundry's Interactive Map. There, it's a bit easier to tell that things are off.
Overall, you can likely tell that the borders of provinces are all a bit muddled:
- Craglorn extends north of the northern border of Cyrodiil, where the Jerall mountains are. Lorewise, Craglorn should be southwest a ways from its current placement.
- Black Marsh and Morrowind are smaller than they should be, and should be a scaled slightly larger in proportion to the other provinces.
- The Rift and Eastmarch infringe upon the Velothi Mountains lore placement, and prevent any future expansion into that part of Morrowind due to incorrect map placement.
- Eastmarch, on ESO's Tamriel map, has a peninsula, but if you look at its internal map, the location held there is high in the mountains. Based upon information from Skyrim (the game) there is meant to be a mountain range surrounding this "peninsula" and on the other side of it should be the land of Morrowind, with the city of Blacklight.
Now, what is a good way to fix most of these issues? Of course, it is a good place to start by referencing the original Tamriel maps, myself recommending this
one from the Imperial Library. Next, I would take a look at the zones internal borders created so far- as I said, these are generally the most accurate. Piece them into their correct placement on the original Tamriel map, and try to find where borders don't meet.
You'll likely find:
- Hammerfell's border is far too wide; Craglorn infringes into both Skyrim and Cyrodiil.
- Skyrim does not have enough land to hold all of it's potential zones.
- Pact zones in general do not flow well with the land's borders- More space would be needed for the Skyrim zones.
A simple fix would be to scale up the size of Tamriel by a marginal amount; Craglorn, even with its placement fixed, still needs to respect the Skyrim & Cyrodiil borders. Once Hammerfell's borders are fixed, proceed to check the newly scaled sizes of Skyrim, Morrowind, and Black Marsh. If needed, extend Skyrim's northern border further, and scale Morrowind and Black Marsh to be marginally larger.
Why is any of this needed?
In the end, we'd simply have more space on the Tamriel map. By having more space, we can have both more zones, or larger zones- a greater area in which content can be created. If the current map stays how it is, there would be quite a few problems for the creation of new zones in Skyrim and Morrowind especially; they physically would have no space to exist. In any case, it would be appreciated if ZOS could acknowledge this- even if they do not have the time or resources to address it any time soon.