Hi @hmccabe 

As far as I know, there is no strict rule for that.
You may feel that your problem is related to one of the following functional areas then you can put your post to that.
 

Perhaps those posts are related to more than one functional area. So it's not necessarily known to functional area 100% accurately. But according to your gut feeling, you can put it to the functional area.
If you feel difficult to decide the exact functional area It's okay to put them in a suitable one as you feel.
If necessary, it will be moved to the correct category by relevant coordinators. 

Another thing to consider would be when there is a technical question in a certain functional area, such as when one is trying to add custom fields or perform custom functions on an object like a Purchase Order, the best forum would be a technical one (Framework) not the functional one (Buying).

It’s also worth noting that the categories may also change. As we grow the forum, we realize we need more defined areas. We started with just a few but have sense broken them into smaller buckets - like having Wadaco and supply chain in their own areas. Or making FSM and PSO separate from service. The advise above is great, but ultimately just make your best judgment call and hopefully your topic ends up in front of the right experts based on the category, tags, and search results. 

thank you for the responses