How to check for points within a polygon without creating a new feature layer

LouieRodriguez

I am looking to create a script that runs through a feature layer of points on a map and sees which points falls within a different feature layer on the map that holds polygons of municipalities. These are both CSV based feature layers and when the script identifies an overlap between a point and polygon, it sets one field in the CSV/dataset to True.

I have seen other arcpy scripts about finding points within polygons, but all involve sending those points to a new feature layer, is there a solution that does not involve this?

jcarlson

You could do this easily enough with the ArcGIS Python API.

from arcgis import GIS, GeoAccessor

# Log in to portal
gis = GIS('your-portal-url', 'user', 'password')

# Get point / polygon layers
polys = gis.content.get('polygon service itemID').layers[0] # or whatever layer index, if there are multiple layers in your service
points = gis.content.get('point service itemID').layers[0]

# Create spatially enabled dataframes
poly_df = GeoAccessor.from_layer(polys)
point_df = GeoAccessor.from_layer(points)

# Intersect dataframes
xs_df = pt_df.spatial.join(poly_df, how='left')

At this point, the xs_df dataframe will have all the points from the input layer, with all the attributes of the polygons joined in.

You mention that both your layers are "CSV based". Are you using python to interact directly with the CSVs, or do you mean the layers were published from CSVs originally? How is your polygon layer storing the geometry, if in a CSV?

The GeoAccessor object (another way of saying "spatial dataframe") can be created from a feature class as well. If you need to read a CSV directly into geometry, you may have better luck using GeoPandas, but I won't elaborate on that as much unless it's actually relevant to you.

Back to the code. The xs_df dataframe has a particular field index_right, referring to the ID of the intersected feature. For points which do not intersect with a polygon, this will show as NaN. (That's "not a number".) In Pandas, we can update the value of a field based on the contents of another field very easily using mask. Since we're just updating a boolean field, we can set the field first to "True", then update all the non-intersecting points to "False".

# Set whole field to 'true'
xs_df['field-to-update'] = 'True'

# Update existing field based on intersection
xs_df['field-to-update'].mask(xs_df['index_right'].isna(), 'False', inplace=True)

 Following this, we can simply export xs_df to some other format. The GeoAccessor can export to other spatial types, but Pandas itself can export out to CSV.

xs_df.to_csv('filepath')

xs_df.spatial.to_featureclass('filepath')