Category Dropdown Order

I use categories for my tasks such as "pending" or "computer." My To Do categories are synced with Outlook and I have categories in Outlook that are not needed in To Do.

What is frustrating is when I click 'Pick a category" in To Do, the categories I use are buried down in the list. I wish there was a way to specify what categories are available in the drop down or at least specify the order. 

How is the order of categories determined in the drop down list?