Quantifying number of overlapping shapefiles using ArcPy with ArcMap

Question

I am using ArcMap 10.7.

I have a multitude of shapefiles representing glacial lakes in different stages of their formation, each shapefile produced using a different climate model as basis. All results displayed looks something like this:

As can be seen, the models do not agree on the extent of the lake formation. The "green model" produced the largest lake extents, the "brown model" the smallest ones. I have used 15 models, each for 4 SSP scenarios and 8 timesteps (so all in all 480 shapefiles).

For each lake part in a given scenario and timestep, I now want to quantify the number of models agreeing on its formation. Using Intersect manually gives me only the areas where the models overlap without any information on how many overlap there. And, due to the number of shapefiles, it is not feasible. So far, I could use a number of for-loops (slow, I know, but I don't have a better idea) to go through every model, scenario and timestep and do the intersect like this:

for i in range(models):
    for j in range(scenarios):  
        for i in range(timesteps):
            shapelist = []
            for shapefile in folder:
                if shapefile.endswith(".shp"):
                    shape_location = os.path.join(folder, shapefile)
                    shapelist.append(shape_location)
                    arcpy.Intersect_analysis(in_features=shapelist,
                                             out_feature_class=os.path.join(some_folder, "intersect.shp"))

But I'm stuck on how to determine the number of overlapping polygons for each lake. Is there another way to use Intersect, or another arcpy-related workflow that I could use?

Do you have access to arcgis pro? (https://pro.arcgis.com/en/pro-app/latest/tool-reference/analysis/count-overlapping-features.htm) — BERA, Aug 26 '21 at 09:34
No, unfortunately not. But that would be exactly what I need! — Florian Mlehliv, Aug 26 '21 at 09:43
Look at the second answer: https://gis.stackexchange.com/questions/119439/counting-overlapping-polygons-from-one-shapefile-using-arcgis-desktop — BERA, Aug 26 '21 at 10:02
Thanks a lot, that helped! I will try out some of the approaches there! — Florian Mlehliv, Aug 26 '21 at 10:42

FelixIP · Answer 1 · 2021-08-28T05:28:21.480

I think you should do it in batches, so output of these:

for shapefile in folder:
    if shapefile.endswith(".shp"):
        shape_location = os.path.join(folder, shapefile)
        shapelist.append(shape_location)
Merge(shapelist,in_memory/MERGED_BUFFERS")
FeatureToPolygon("MERGED_BUFFERS", "INDIV_POLYGONS")
FeatureToPoint("INDIV_POLYGONS", "id_point", "INSIDE")
GenerateNearTable(in_features="id_point", near_features="MERGED_BUFFERS", out_table="in_memory/NEAR_TABLE", search_radius="0 Meters")

Will give you a table:

Frequency of 1st highlighted fields will give you count of overlaps for each INDIV_POLYGONS.

This only works when merged boundaries of 2 polygons create 2 or 3 polygons

If this is not the case, e.g.:

you have to create multipoints first:

SpatialJoin("id_point", "MERGED_BUFFERS", "id_point_SpatialJoin", join_operation="JOIN_ONE_TO_MANY", join_type="KEEP_COMMON", field_mapping='FID_A_Merge "FID_A_Merge" true true false 0 Long 0 0 ,First,#,id_point,FID_A_Merge,-1,-1;ORIG_FID "ORIG_FID" true true false 0 Long 0 0 ,First,#,id_point,ORIG_FID,-1,-1', match_option="INTERSECT", search_radius="", distance_field_name="")
Dissolve("id_point_SpatialJoin", "id_point_SpatialJoin_Dissolv", "JOIN_FID")

and proceed with NEAR TABLE as described above:

Quantifying number of overlapping shapefiles using ArcPy with ArcMap

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