https://sims4studio.com/thread/2087/cas-uv-1-template-images

These templates are to help map the uv_1 for CAS meshes. To use them you will need to scale your uv_1 to 0.5 on the X axis so that it will fit in the grid. Before importing your mesh back into Studio, remember to scale your map back so that the right half is on the grid and the left half is off the grid.

Templates:

Adult Male

Adult Female

Toddler:

How to use the templates:

This will get an EA style uv_1 onto the template that I have posted. When your mesh has a uv_1 that you are satisfied with, you can reverse the steps in the last picture. Instead of scaling by 0.5 to make it half size, you scale by 2 to make it double size again. And instead of moving it to the right with 512, you can move it to the left with -512. The result will be that your uv_1 should look more like the second picture with half of it off the image.

Marking Seams:

With a new mesh starting from scratch, you will need to mark your UV seams before unwrapping. This is a reference image showing where a standard uv_1 from EA will have its seams marked. The seams are the orange lines on the mesh.