Analyzing and presenting change of 60 years

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10-04-2022 07:52 AM
nikeldas
New Contributor

I'm at a point in my master thesis where I don't really know what to do and it's: tadaaa - about statistics.
The thesis is about a comparative vegetation mapping.

I mapped a large area phytosociologically and according to a certain systematics.
The area has been mapped according to the same systematic 30 and 60 years ago as well. So now I can see and analyze the changes (climate change, overfertilization etc.). Of course, the whole thing runs digitally supported with a geoinformation system (ArcMap 10.8).

Here's the problem:
I have three phytosociological mappings from the same area. Two historical ones from the 60s and 90s and my current one.
I have all digitized as vector data (polygons) in ArcMap.
My goal is to somehow statistically capture the change.
For this I can
1) look at the overall balances of the various plant communities (e.g., bristly grass lawns have declined in favor of intensive grassland taken as a whole). I can just so manage calculating that :D.
2) Consider the individual areas of the different biotope types in the sense of "which areas have developed where". Because this consideration falls out in a total balance of 1). For example, if an area has developed over the years from a bristly grass lawn to a rich meadow, but on another area vice versa, this development is lost in the overall balance of 1).

Now I calculated a grid of points over the areas and got about 83.000 points with the respective information about the mapping units of the 3 time slices (coded as numbers [short integer]).
But now I struggle with the evaluation of these points.
Can you think of a suitable representation for the change? I want to see how many points have stayed the same over the years, how many have changed and HOW they have changed.
I'm thinking of both a statistical and a cartographic solution.

Hope it's reasonably clear what I'm getting at. It's actually kind of about a measure of change.

Lovely greetings and thank you 🙂
Nik

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1 Reply
JohannesLindner
MVP Regular Contributor
  • intersect the points with each polygon layer
  • join each output to the points
  • export to a new feature class, delete unneccessary fields
  • -> now you have a point feature class with 3 codes per point
  • Calculate Field
    • calculate 3 text fields: "Code1 -> Code2" or "No change" for 60s/90, 90s/2020s, and 60s/2020s
  • For each of those fields, use Summary Statistics to get the count of points
  • multiply with your point area to get the total area for each change

Have a great day!
Johannes
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