Hi LaVerne, thank you for writing to the Ask an Expert Forum. I'm sorry to inform you that I do not have a reference to provide. What I can supply is my own personal opinion. If this map was produced as shown in this print example and was not divided for a specific reason, “reference points” are not necessary. Adding labels to areas that do not exist in print can be misleading or inaccurate. At the same time, as a TG artist, you wouldn't surround this continent in water, for example where Canada exists, which can lead the reader to interpret this area to be an island rather than a continent. However, if the image or the context leading up to it does not introduce this map as "North America or The U.S." you can add this information within a transcriber's note for orientation.
Hope this helps.