UKTC Archive

Re: Tree canopy cover as a sustainability metric: Planning for the future - consultation

Subject: Re: Tree canopy cover as a sustainability metric: Planning for the future - consultation
From: Jon Heuch
Date: Sep 25 2020 16:58:26
Brynley

 

i)                    You can’t measure accuracy! (that is - from sampling).

ii)                   Please provide me with a reference that suggests they
are estimating something to “2%”.  If they do have a measure it will be of
precision. Something very different to accuracy. If you apply more sample
points your precision increases & that appears to give you a good measure.
But it doesn’t because of the problems I describe.

iii)                 CAD will very accurately measure what you put into CAD.
That is not the problem. If you draw a circle around a tree, CAD will do a
wonderful job of telling you the area of the circle. The first big problem
is that images have shadows, varying from image to image; if you are dealing
with only one image, there will at least be some uniformity across the
image. The second is that trees are not uniform cylinders, spheres or other
shapes so whatever you measure, however you measure.

 

You might want to read the musings of Francisco J. Escobedo (used to work
with I Tree; Google Scholar gives you an entrée to his work) who gave a talk
at the AA conference in 2016. He at least started to discuss some of the
statistical issues related to inventory of the urban forest. I can tell you
simply you won’t pick up modest but real changes in canopy cover!
Undoubtedly you will generate numbers. Undoubtedly they will be different.
Will they be meaningful? Most unlikely.

 

Jon 

 




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