This is the second of two steps that allow you to reduce the number of documents retrieved by narrowing the scope of your search. The number of documents you will retrieve for any subheading you choose is displayed in a column to the right of the subheading name. If you are unsure what each subheading means, read the explanatory text which appears in the panel to the right. As you scroll through the list of subheadings, the description for each is displayed. If the text in the subheading description takes up more room than is available in the description box, use the TAB key to toggle to the description and use the up or down arrow keys to scroll.
TAB also moves the cursor back through all the options to the list.
Now you're done with Mapping, and your results are posted to the Main Search Screen. After following the various steps of the Mapping process, you'll find the precision and usefulness of your results superior to merely performing a textword search on the term.