Several countries have borders that follow lines of latitude or longitude, including Libya and Sudan using the 20th parallel, Egypt and Sudan using the 22nd parallel, and Mauritania and Mali using the 25th parallel.
Here's a more detailed breakdown:
Latitude as Borders:
20th Parallel: A short section of the border between Libya and Sudan, and within Sudan, the northern border of the Darfur region.
22nd Parallel: Much of the border between Egypt and Sudan, partly disputed (see also Hala'ib Triangle).
25th Parallel: The northernmost section of the Mali-Mauritania border.
31st Parallel: The border between Iraq and Iran.
17th Parallel: The division between Republic of Vietnam (South Vietnam) and the Democratic Republic of Vietnam (North Vietnam) during the Vietnam War.
15th Parallel: A de facto maritime border between Honduras and Nicaragua.
While less common, some borders also follow lines of longitude, particularly in areas with straight or relatively straight coastlines.
For example, some sections of the border between the United States and Canada follow lines of longitude.
Wyoming, Colorado and Utah have boundaries that are latitude and longitude.