After some small effort I have managed to acquire an aerial-photo ('Where It All Lives' - right) of the Walloon Estate from Google Earth and overlay it with a 2x2 grid that I hope will ease the task of describing where things are as I find them.
(I read on Google Earth's website that:
"You can personally use an image from the application (for example on your website, on a blog or in a word document) as long as you preserve the copyrights and attributions including the Google logo attribution. "
- so there seems no issue with me doing this.)
Henceforth, when describing where things are, I'll quote a grid-reference, quoting a horizontal coordinate, followed by vertical coordinate. So for example, at grid reference (1.1,1.5) you're looking straight down onto the Bramley Apple tree that sits in the middle of my lawn.