Yes, this is confusing.
There are just over 50 Sectional Chart maps that cover the continental United States, Alaska, and Hawaii, each one named for a city on the map. And these charts are updated every few months with the latest information from the FAA.
Traditionally, you would buy a paper version of a Sectional Chart, but these days most drone pilots are using apps on their computer, tablet, or phone to conduct airspace research.
And in the test supplement, when you’re looking at the images, it’s a small snapshot of the entire Sectional Chart, so you won’t get to see anything on the border.
As an example, check out an airspace research tool like https://skyvector.com
You can isolate the actual Sectional Chart for a particular region in order to view information on the border of that chart.