Python Shapely Cant Find Points Within Polygon When Looping Polygons

Question

I have a csv file of store locations with lat and lon. I also have a geojson file with polygon features of US Census tracts. I want to use Python to see in which polygons each location exists.

I am using Shapely Python library's contains() to loop through the csv file of store locations, grab lat and lon coordinates, and then check if the coordinates exist within one of the polygons from a geojson file.

The code I have works successfully if I loop through each location/coordinate first, then loop through each polygon, using contains() or within() to check if a polygon contains the point.

But this is too slow, so I want to inverse the process and loop through the polygons/geojson file first, and check the hundreds of thousands of polygons against the thousands of coordinates, instead of the other way around.

However, when I simply switch the loops to check the polygons against the coordinates, contains() does not find any matches, even though it finds correct matches when I loop through coordinates first and check them against polygons. It's the same code, except reversed.

Code (contains brings up false):

with open(mapFile) as f:
    data = json.load(f)

    #Loop through features in Geojson file
    for feature in data['features']:

        polygon = shape(feature["geometry"])

        for row in locationsFile:
            #get point coordinates from file
            pointLat = float(row[13])
            pointLon = float(row[14])

            point = Point(pointLon, pointLat)

            print(polygon.contains(point))   
            if polygon.contains(point):

                #Grab data
                newx = feature["properties"]["x"]
                newy = feature["properties"]["y"]
                newz = feature["properties"]["z"]
                #append data
                row.append(newx)
                row.append(newy)
                row.append(newz)
                #update file
                newFile.writerow(row)
                break

This code produces accurate results:

with open(mapFile) as f:
    data = json.load(f)

    #Loop through coordinates in CSV file
    for row in locationsFile:
        #get point coordinates from file
        pointLat = float(row[13])
        pointLon = float(row[14])

        point = Point(pointLon, pointLat)

        #Loop through features in Geojson file
        for feature in data['features']:

            polygon = shape(feature["geometry"])

            if polygon.contains(point):

                #Grab data
                newx = feature["properties"]["x"]
                newy = feature["properties"]["y"]
                newz = feature["properties"]["z"]
                #append data
                row.append(newx)
                row.append(newy)
                row.append(newz)
                #update file
                newFile.writerow(row)
                break

Answer 1

break will behave differently in both cases. It will only break out of the innermost loop, which in the "correct" case, is the loop through data['features'] , but in the incorrect case, is the loop through locationsFile