Edit 06/30/17: Updated for Patch 7.3
Now that the Minimap of the Broken Isles has shown up, I've decided to make some measurements with it and show how it holds up
compared to other continents.
This is just for fun and a way to provide some scale, not an xpac1 vs. xpac2 kinda thing.
Also keep in mind that we're looking at an unfinished map, meaning that the shape of zones might change and the possibility of
other islands being added throughout content patches.
Other than that of course: Bigger doesn't always mean better.
Certain scenes require more work by the artists, others not so much.
Huge empty fields like this desert in Uldum or this place in Icecrown help increasing the size of a zone,
yet there is visually not much going on.
Especially since MoP there is a noticeable improvement in terms of 'Level of Detail', content density and general polish,
so all these things have to be taken into consideration.
Moving on.
Measuring the size of continents is a simple process. Rather than making weird ingame distance approximations, all calculations are
based on minimaps which are extracted directly from the client and then assembled. You'll end up with a big .png file.
Unlike Worldmaps, Minimaps are not hand-painted but generated using actual terrain data. Everytime Blizzard makes noticeable (even small) changes to the world, they'll generate and deploy new minimaps for affected zones.
The most important thing though: Minimaps all have the same scale. Meaning a 100px distance on one map equals the same distance ingame as a 100px distance on another map.
You can verify this yourself by traversing a zone while measuring the time it takes you to get from one point of your minimap to another. Use the image editing software of your choice to measure the distance in pixels between those two points of your minimap. Basic math will now get you the distance you've traveled in px per 1 second. Do the same thing on a different continent and you should get the same value, proving that in fact both minimaps have the same scale.
Since this is the case, once we get the pixel count of a given zone - representing the surface area - we can easily use this number for comparisons.
Now to get the pixel count of a zone we can use Photoshop or other image analytic tools. However first the minimap image needs to be croped so that we only measure the landmasses and not the ocean and other non-relevant areas. I've also cut out PvP-only zones like Ashran or Wintergrasp as I consider those the same categoty as battlegrounds.
Removing the entire ocean isn't entirely fair considering it's often also part of the player experience but we deal with it for now.
The cropping process doesn't need to be perfect - a tolerance of about 0.5% is pretty acceptable imo.
Beneath is the result of this process. It's a downsampled version since I'm not able to upload a 400 gigapixel image.
New race/class zones as well as patch zones were also factored in and marked in different colors. Although I intentionally left out Thal'Dranath since it's just a very raw shape atm and will probably have a different shape when it gets released.