How was this human head UV map created? How can I make it square like that?
Welcome 
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Properly with a seam at the centre of the backhead, than “simple” unwrap and some rotatotioon and then..
I have an ancient method that I created to unwrap the makehuman base before we had proper UV tools, which would work for this purpose, but might not be the best choice. In edit mode, add a subdivided square with no faces. >> position the square within the face mesh. >> make a new shape key >>with proportional editing enabled, scale the square up, so it “grabs” the face and stretches it into a square shape. Then with the face facing you in the viewport, hit U and unwrap it with the “project from view” option. Return to the basis shape key and delete the square.
I almost forgot to mention…the smooth vertices function is also needed during the process.
Thank you for your reply sir. In the image I sent, the mouth, nose, and eyes remain undistorted (it looks as if “Project from View” was used); how can I achieve this?
I don’t understand why you would want the nose to remain undistorted, because ideally all the faces that are being unwrapped should face more or less forward. otherwise the texture will be stretched on the steep parts.
I don’t know maybe to use a pre-made texture I created in Photoshop
It will require lots of manual adjusting in the UV editor using proportional editing ( of UV coords ) IMO, or you could try baking the texture from the original model onto the coords of the new one to start with.
ok thanks 
Maybe for this kind of unwrapping also Cylinder Projection might be “helpful” but with some further “corrections”..
I recall that UV type being called ‘spherical’ in the FaceBuilder wiki. I’ve seen Valve use it for most of their head textures in Half-Life 2 as well, here’s a few.
The purpose of these UVs is to use the most that texture map can offer, that’s why they are usually done in 2:1 aspect ratio (1024x512/2048x1024/4096x2048) but they are also able to be done in 1:1, it depends on your texel density goals.
I usually do my heads in that style. The thing is though I don’t use Blender for it, I prefer using RizomUV on my workflow, here’s how I do it there.
- I do a simple unwrap in Blender, notice the very simple seam here. It should start from the neck and end on the top of the cranium.
- I export the model and I load it up on RizomUV, then I start by constraining the vertical edges of the head itself and then constrain the horizontal edges after.
- Hit CTRL+A to select the entire UV, disable Prevent Overlaps and hit Optimize. I usually do it 3 or 6 times till it looks straightened enough. The less stretch there is, the better. Then hit Squarify.
That’s it. But notice that I left out the mouth and eye interior when I brought it to Rizom. That’s because I personally prefer hiding it in the UV openings, less of a headache when baking personally
EDIT: You should smooth the corners of the scalp region if your character is bald or has short hair. The human scalp alone cannot be square under any circumstances, make it a falloff.
You can probably use Mio3 UV or Zen UV (blender addons) instead of Rizom. The workflow should be very similar. There is also UVLayout
Thank you for your answer it was very helpful