create diversity map of qualitative features, ArcMap

Question

I am trying to create a map of forest type diversity with ArcMap. I have a polygon forest layer with the different forest types as attributes (e.g. 0815, 0862, 0813, ..., which stands for 'mixed forest', 'oak forest', and so on.)

Using Patch Analyst I have created a Hexagon map and intersected it with the forest polygon layer. Usually I would now use 'field statistics' to calculate the variance of forest types for each Hexagon field and then join the result table to the Hexagon polygon layer to create a diversity map. Calculations don't work, however, since I have qualitative Features instead of quantitative ones.

Does somebody have an idea how to do this?

Answer 1

I solved the Problem:

1. dissolve forest data according to forest type
2. create Hexagons
3. join forest data to Hexagon ('spatial join')

--> this gives me what I want, in the new table there is a Count_ field that Displays not the number of Polygons, but the number of different forest types in the hexagon

Answer 2

With qualitative data, "variety" is the closest match to variance. In other words, you need to count the number of different classes within you hexagon. If you create the intersection between your hexagons and your forest layer, you will have a new feature class with the ID of hexagons and the values of your forest layer. Then you can summarize your table to have the count of polygon inside each hexagon: this is the variety.

Answer 3

You could get the area of each polygon (using 'calculate geometry' in the attribute table by right-clicking on a field heading) if these haven't already been generated in patch. You could then concatenate the forest type and hexagon id using the field calculator (=[hexid] &"" & [foresttype]). Then 'summarize' (right-click on the field name, and go to summarize...) and select stats for the area field. this will generate a list of every hexid and forest type, along with area data for each, and a count of each time a forest type occurs per hexid. split the hex/forest field by the '' character in Excel, and you can enter the data into a pivotTable and get summary statistics for the number and area of each forest type per hexagon, the average size, and the number of different forest types in each hexagon. you should be able to use that data to derive some richness/diversity value