Alex,
"need" is a most strange expression in this context.
People, myself included, have been camping for thousands of years before GPS was even thought about. I have always used ordinance survey maps and never had a problem. This said, some mobile 'phones do have GPS built into them but, on the other hand, they will give you no indication of what the surrounding countryside looks like.
Try map reading - it's more fun.
Blessed be
Karma Singh