Simplify the following text for a Grade 12 native English-speaking person.
Original: The surrounding Kalahari Basin covers over 2500000 k extending farther into Botswana , Namibia and South Africa , and encroaching into parts of Angola , Zambia and Zimbabwe .
Simplified: The surrounding Kalahari Basin covers over 2.5 million kmÂ extending farther into Botswana , Namibia and South Africa , and encroaching into parts of Angola , Zambia and Zimbabwe .