Arcpy: what tools are most suited for this job?

Question

I'll try to be as much detailed as possible but please let me know if anything is missing:

I'm trying to get the number of lines in layerA that intersect with each line in LayerB and stores that number of intersections in a field in LayerB for each line, or row in tabular format. Both layers are huge and complicated loops may be problematic, but share your opinion please

the following is my logic:

-For each row in LayerB's Attribute table : ->Select(currentRow)->makefeature(currentRow)->selectByLocation(all lines that intersect with currentRow)->getCount(selected)->CalculateField(getCount)

will that theoretically work, please help me as I'm new to both arcGIS and python.

Answer 1

It is clear that we want a count of intersecting features from layer A, written to a field in Layer B - I agree the approach you've shown here should theoretically work, in terms of the conceptual steps you have sequenced to arrive at your answer.

As an alternative though, maybe you could run a spatial join using the INTERSECT rule, and look at the JoinCount field in the output layer:

import arcpy
from arcpy import env

env.workspace = "Your\\Working\\Folder\\Path"

LayerA = env.workspace + "\\" + 'TheFirstLayer.shp'
LayerB = env.workspace +  "\\" + 'TheSecondLayer.shp'

arcpy.SpatialJoin_analysis(LayerB, LayerA, "OutPutLayer", match_option = 'INTERSECT')

We can then check the 'Join_Count' field in "OutPutLayer" to view the count of LayerA features INTERSECT-ing LayerB.

Best Luck Yo.

Also - you mentioned you're 'new to arcpy' - arcpy is cool. As an aside, the syntax match_option = 'INTERSECT' is called supplying a 'keyword argument' - it lets you skip around the order of optional arguments when calling a tool like arcpy.SpatialJoin_analysis()

Answer 2

Your logic is fairly close, here is what I would do:

1. Make feature layer on layer A and B
2. Use update cursor on layer B, (make sure you pull in a unique id field or FID column to query against AND the field to store the layer A feature count)
3. Loop through table and use unique id value from step 2 to select layer by attribute (new selection method)
4. While in loop, use select layer by location (new selection method) against step 3 layer to layer A feature layer
5. Use get count method for layer A
6. Update layer B selected row with step 5 count value (cursor.updateRow(row) method)

Answer 3

Your intuition is correct, and the steps you've laid out will work. Doing this with an arcpy.da.UpdateCursor (ArcGIS 10.1 or later) will make the logical flow pretty simple and straightforward. Something like this:

with arcpy.da.UpdateCursor(layerA, ['SHAPE@', 'COUNT_FIELD']) as cursor:
    for row in cursor:
        arcpy.SelectLayerByLocation_management(layerB, 'INTERSECT', row[0])
        row[1] = int(arcpy.GetCount_management(layerB).getOutput(0))
        cursor.updateRow(row)

Depending on the size of your feature classes, this may take a long time to run, but that's going to be pretty hard to avoid no matter how you approach the problem.

Answer 4

your workflow would theoretically work, except that select by attribute works with a layer, so you need to run makefeaturelayer before select by attribute.

However, note that what you need can be done with the built in spatial join function.