"The wood that local people call Fagley Wood"

I was looking at the Google map of where I grew up, and was somewhat perturbed to see that what we all referred to as Fagley Wood or Fagley Woods is three separate woods, called called Bill Wood, Round Wood and Ravenscliffe Wood.

So Fagley Wood as such does not exist but everybody calls it that. I think that most people add the "s" to "Wood" because clearly the whole wood can be divided into three smaller areas, which are nonetheless contiguous. Notwithstanding that Fagley Wood is a daft name for it, because Fagley proper is way off the southern end, why on earth did they bother thinking up new official names?

Which reminds me that my Dad once wrote to the Ordnance Survey people to point out that their map had swapped over the names of two hills up north somewhere (I can't remember where they are or what they are called). So what local people called Hill A was labelled Hill B on the OS map and vice versa. The OS wrote back and told my Dad that it was the local people who had got the names the wrong way round, and they had no intention of changing their map.

All most puzzling.