[GIS] How to determine which polygons, if any, points fall within

arcgis-desktopqgis

I am a amateur at GIS and need some help. I have a group of shapefiles of various areas and an Excel spreadsheet of addresses I have geocoded to points. I want to determine whether each point falls within the boundary of a shapefile, and which feature within the shapefile it falls within.

For example I have:

Shapefile Zone: polygons Zone #1, Zone #2, Zone #3, etc.
Shapefile Area: polygons Area #1, Area #2, Area #3, etc.
Shapefile Address: points Address #1, Address #2, Address #3, etc.

For my results I would like it to list:

 Address           Falls within feature
Address #1     Zone #2, Area #1
Address #2     Does not fall within any feature
Address #3     Zone #3

I know how to incorporate all the polygon features into a shapefile but not how to have it identify what polygon features of the shapefile each point falls into.

I am using ArcGIS and Quantum GIS. So in summary my issue is taking coordinates and determining if they fall within certain polygon shapefiles I have. The goal in the end is to start with a list of geocoded addresses (points) and end with a determination of which (if any) polygon's each point falls in.

Best Answer

For quick and simple geocoding you can use CartoDB's service. You'll need to make an account but it's free and you are allotted 250 free geocodes a month. You can export your geocoded addresses as a shapefile from there. Then in QGIS you can join data from your polygon layer to your points layer by doing a spatial join (Join Attributes by Location in QGIS) and this will add whatever fields from your polygon layer to your points layer. So for instance if you have a field for "Zone #" and a field for "Area #" you can use the spatial join tool to add these attributes to the point that falls within those. Here is a pretty good tutorial on spatial joins.

Related Solutions

[GIS] Exporting query to identify what polygon certain points fall in using ArcGIS Desktop

artwork21 is absolutely right. Another way to do that is to:

Right click on the point feature class (your street addresses) and go to Join and Relates > Join.
In the prompt box, at the top, select the drop down and choose "Join data from another layer based on spatial location".
Select your polygon feature class (districts) and choose "it falls inside". This will export a shapefile that contain every point and the district it falls in and then, as artwork21 mentioned,
export the resulting table as a .dbf,
open it with Excel and save it as a .csv.

You can also reverse this for further analysis:

Right click the polygon shapefile > Joins and Relates > Join.
Select "Join data from another layer based on spatial location"
Choose the point feature class as the joining layer.

This gives you a few more options. For example, you can give each polygon attributes of Average, Minimum, Standard Deviation, Sum, Maximum, or Variance (or all of them) from the point feature class.

So, if you were wondering how many addresses are assigned to the "xyz" district, this would be an ideal solution.

You can also do point to point. For example, if you have a point feature class with distribution centers, and another point feature class with store location and you want to see which which distribution center every store is closest to, you can:

Use the Store Location feature class and join the distribution center feature class
Choose "each point will be given attribute of joining layer closest to it.."

The output will show every store and the attributes of the distribution center to which it is closest to.

[GIS] Move Incorrectly Placed Address Points to Correct Parcel

The following (untested) code should do the trick. This first gets the geometry of the points and polygons into dictionaries, then uses the polygon dictionary with the contains method of the arcpy.Polygon to test if the correct point is inside it. If not it is added to a new dict and used to update the point geometry.

import arcpy

def move_points(addresses, pt_pin_field,  parcels, parcel_pin_field,):

    # get address geometry
    with arcpy.da.SearchCursor(addresses, [pt_pin_field, 'SHAPE@']) as rows:
        point_geom = {r[0]: r[1] for r in rows}

    # get parcel geometry
    with arcpy.da.SearchCursor(parcels, [parcel_pin_field, 'SHAPE@']) as rows:
        par_geom = {r[0]: r[1] for r in rows}

    # move geometry dict
    move_dict = {}
    for pin, pt in point_geom.iteritems():
        if pin in par_geom:
            if not par_geom[pin].contains(pt):
                move_dict[pin] = par_geom[pin].centroid

    # loop through address points and move if point pin doesnt match spatial join pin
    if move_dict:
        with arcpy.da.UpdateCursor(addresses, ['SHAPE@', pt_pin_field]) as rows:
            for row in rows:
                if row[1] in move_dict:
                    row[0] = move_dict[row[1]]
                    rows.updateRow(row)           
    print 'moved {0} points'.format(len(move_dict))
    return

if __name__ == '__main__':

    addresses = r'C:\path\to\address_points.shp'
    add_pin = 'Address_PIN'
    parcel_pin = 'PID'
    parcels = r'C:\path\to\Parcels.shp'

    # run it
    move_points(addresses, add_pin, parcels, parcel_pin)

Related Question