Questions about uv map

[Zijian007]

Hi, thank you for you awesome work! I am a beginner of computer vision and computer graphics, and I have some confusion about uv map.
1: How to construct the template texture map when you prepare IUV maps?
If I understand correctly, in the texture map of fig2, the horizontal and vertical axis are uv coordiantes, and the value in the pixel is the SMPL vertex coordinate corresponding to uv, so how to construct the texture map? And why the layout of body parts in this texture map is different from the layout of texture map in Densepose paper？Is there an explicit correspondence between uv coordinates and vertex coordinates？Like u,v=f(x,y,z)