Census could still have asked about gender identity as well
As far as I know it still does.
This census is going to really fuck things up for trans people.
Some trans people will answer the sex question as their birth sex, and others how they identify, depending on their point of view.
The gender identity question is voluntary so some will answer and some won't.
The net result will be that it will not be possible to establish how many trans people there are in Scotland and whether they are transmen or transwomen. With such a small population this is going to be a massive problem with planning things like trans healthcare.