How to show how many layers (polygons) overlap with a colour sheme?

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05-16-2020 08:15 PM
MauriceKasprowsky
New Contributor II

Hey,

I am planning to create something like a biodiversity map on ArcGIS Pro. For that purpose I downlaoded the shapefiles for the range of various species, in form of polygons. Now I am planning to merge all this data together. Basically, what I am trying to do is to colour the map differently depending on how many layers (polygons) are overlaying in one area (e.g. the more overlay the redder). Meaning I am trying to show how many species are found in a certain area. Is there any tool that can do this. I was playing a round for a while but didn't find anything.

On top of this I would also like to include the RedList threat level for every species (i.e. layer) in the attribute table, in form of numbers the higher the more endangered. With those I then would liek to create a second map showing the accumulated threat level in certain areas, so once again showing different colour (e.g. the higher the accumulated threat level the redder the area). Generally I have amn idea how to do it but I would first have to create those overlapping layers, and then I would be wondering how to calculate the accumulaed threat level number.

I hope everything is clear and someone can help me out.

Thanks a lot,

Mo

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MervynLotter
Occasional Contributor III

Hi Mo

As of ArcGIS Pro 2.5 you can now use a new geoprocessing tool called Count Overlapping Features. Do check out Count Overlapping Features—Help | Documentation  for more details.
Mervyn

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5 Replies
MervynLotter
Occasional Contributor III

Hi Mo

As of ArcGIS Pro 2.5 you can now use a new geoprocessing tool called Count Overlapping Features. Do check out Count Overlapping Features—Help | Documentation  for more details.
Mervyn
MauriceKasprowsky
New Contributor II

Hi Mervyn,

Thanks a lot! I just had to update my GIS and then I found the tool and it worked really well. Do you have an idea how I could include the threat level in this as well. Like for every species layer (polygon) I have the threat levle as a number in the attribute table. If they were Rasters I could simply do Raster calculation but since they are Polygons I do not know how to add the values together. Also I would then need to display how high the accumulated threat level of the overlaying layers is, rather than showing how many layers are overlapping.

Thanks a lot,

Mo

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MervynLotter
Occasional Contributor III

Hi Mo

I am not sure exactly what you mean by threat level but I suspect it may be something along the lines of, hypothetically: Critically Endangered (CR) = 20, Endangered (EN) = 10, Vulnerable (VU) = 5, Near Threatened = 1. If so, then I suggest you try:

  1. Running the Count Overlapping Features tool only on a group of similar threat layers, like only on the CR layers. Then do the same for each of the other threat categories. 
  2. Then add a new field to the attribute table for each outputs of the Count Overlapping Features and call this new field "score" and use Calculate Field to calculate the score for each output (Score = !Count_! * 20) (or whatever your threat weighted score is)). So at the end you will have several polygon datasets each with a "score" field that is a combination of the count of overlapping features multiplied by your threat weight.
  3. Next run a Union on these polygon features. If you dont have an advanced license you may need to run this tool several times until all your polygon layers are in one layer. An advanced license can take several files as input features at one time.
  4. Then add a new field to the output of the Union GP tool and call it "CombinedScore"
  5. Use Field Calculator to add up the respective "score" fields. (CombinedScore = !Score! + !Score_1! + !Score_2!)
  6. So in the end you should have a weighted threat score field which you can symbolise and prioritise. 

Is this what you are looking for?

Good luck and let me know if it worked or if you require a different process and I misunderstood your need. 

I do think this process may be easier in raster. 

Mervyn

MauriceKasprowsky
New Contributor II

Hey Mervyn,

Yes exactly basically how endangered which species is.

Thanks a lot I basically followed your advice just tweeked it a bit. I left out the count overlap in the beginning. Because I want to produce two maps. One for how many species can be found in an area (for this I use the count overlap tool) and then one map with the accumulated threat level of all species in one area (e.g. S1 (lv. 3) + S2 (lv.4) + S3 (lv.3) + S4 (lv.2) + S5 (lv.2)). So if I would use the count overlap before hand and combine all species from one threat level I assume I could not add up the threat levels of each species invidually anymore? Either way also just doing the Union and then the Field Calculator gave me exactly the result I needed.

Thanks so much for your quick and amazing help!

All the best,

Mo

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MervynLotter
Occasional Contributor III

Excellent, glad it worked.

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