This map of Kenya will give you an idea of the country. Notice that the equator runs through it. Lake Victoria, setting for the movie The African Queen, is on the southwest. Nairobi is the capital and largest city. Lake Turkyana in the north.
Water is black, land is dark blue in the photo.
Nairobi is the large white spot in the lower center. Only areas without light would be remote enough for Survivor including anywhere in the north and along the southern border. In this map the lighter colored areas are less populated. Vegetation dictates the background scenery of the Tribal Camps and Tribal Council. Consequently, it may or may not be filmed on a true savannah.