Creating individual buffers based on specific values of one attribute using ArcPy with ArcGIS Pro

Question

I am using ArcGIS Pro.

I have a road shapefile with an attribute named 'Type' which has different values ('Highway', 'Main Road' etc.).

I want to create different buffers based on these values e. g. buffer all objects which are "Type = 'Highways'" by 5 meters, all objects which are "Type = 'Main Roads'" by 3 meters.

Here is my code so far:

roads = r'C:\Users\roads.shp'
arcpy.MakeFeatureLayer_management(roads, 'roads')
    
with arcpy.da.SearchCursor(roads, ['Type']) as cursor:
    for row in cursor:
        if row[0] == 'Highway':
            arcpy.Buffer_analysis(roads, 
                                  r'C:\Users\buffer_highway', 
                                  '5 Meters', "FULL", "ROUND", "LIST")
        elif row[0] == 'Main Road':
            arcpy.Buffer_analysis(roads, 
                                  r'C:\Users\buffer_main_road', 
                                  '3 Meters', "FULL", "ROUND", "LIST")

If I run it, hundreds of buffers are created (the buffer is executed for the whole shapeifle evertytime one of the cursor meets the condition of the if-statement).

I also tried this to buffer each value separately:

if arcpy.SelectData_management(roads, "Type = 'Highway'"):
    arcpy.Buffer_analysis(roads, r'C:\Users\buffer_highway', 
                      "5 Meters" , "FULL")
else:
    pass

But I get this Error:

ExecuteError: Failed to execute. Parameters are not valid.
ERROR 000840: The value is not a Data Element.
ERROR 000840: The value is not a Composite Layer.
Failed to execute (SelectData).

Has anyone a suggestion?

Answer 1

Add a new (number) field to the feature class that holds the buffer distance for each feature. Use the field calculator to populate this new field according to the Type value.

Then when buffering, instead of using a distance value, tell it to use this field instead.

The name of the Buffer parameter is "buffer_distance_or_field". Ie, you can enter either a distance number, or a field name. If you use a field name, it will look up the number in that field for each feature.

See: https://pro.arcgis.com/en/pro-app/latest/tool-reference/analysis/buffer.htm

If the data in the feature class changes regularly and you don't want to have to keep re-calculating the buffer distance values every time you want to create the buffers, you could use a seperate table for the types and distance values to look up, and then join the feature class to this table (instead of adding a new field to the feature class).

Answer 2

I don't think you can use the Geoprocessing Tools as you have, in an "IF" statement in the second example. In the first example, you are telling ArcMap to Buffer the roads everytime if finds a "Main Road" or "Highway" in the Type field of the shapefile.

I don't have access to ArcGIS / Pro to test, but find a workflow below:

1. Select the highway (using arcpy.SelectLayerByAttribute and arcpy.analysis.Select)

2. Buffer highway

3. Select Main Road

4. Buffer Main Road

5. Merge all buffered roads to one feature

   hwy = arcpy.management.SelectLayerByAttribute(roads, 'NEW_SELECTION','"type" = "Highway"')
   hwybuf = arcpy.analysis.Buffer(hwy, hwybuf, "5 Meters")
   mainroad = arcpy.management.SelectLayerByAttribute(roads,'NEW_SELECTION','"type" = "Highway"')
   mrbuf = arcpy.analysis.Buffer(mainroad, mrbuf, "3 Meters")
   arcpy.management.Merge(["hwybuf", "mrbuf"],"C:/output/Output.gdb/allroadsbuffer")

As I said, untested, but I think you will get your results by splitting the select by attribute out first, buffer, then merge it back together.