The 1st parallel south is a circle of latitude that is 1 degree south of the Earth's equatorial plane. It crosses the Atlantic Ocean, Africa, the Indian Ocean, Southeast Asia, Australasia, the Pacific Ocean and South America.
The parallel defines most of the border between Uganda and Tanzania, and a very short section of the border between Kenya and Tanzania.
1st parallel south Wikipedia
Starting at the Prime Meridian and heading eastwards, the parallel 1° south passes through: