Adding random spatial error to addresses using python?

MichelleDeBartolo-Stone

Hi.  I have geocoded a list of ~2,500 survey respondent addresses and now want to add random spatial error to each location based on underlying population density while also retaining points within their original census block and keeping points out of water bodies.  I am not familiar with Python and am wondering if this is something I could do using Python within ArcGIS 10.2.  ...or maybe there is a better way?   

Development varies from urban to large tracts of rural areas- and geocoding addresses to the census block centroid isn't ideal in the rural areas. 

Essentially, my thoughts are:
(1) Add random spatial error to each point: 360 degrees, distance based on population density.  e.g. if pop. density is < 1 person/sq mile, then distance offset would be within 2 mile radius; if pop. density is 1 < x < 50, then distance offset would be within 1 mile radius...
(2) Keep point within the boundary of the census block from which it originates
(3) Keep point out of water bodies.

I appreciate any thoughts, advise, help that may be offered.  Thank you.
Michelle

MichelleDeBartolo-Stone

Hello Michelle,

You should first prepare your census and address feature classes (this can be done without Python):

• Remove water bodies from census with Erase
• Add a field representing the radius of the buffer to census, and calculate it based on the population density field
• Join the radius field to the address fc with a Spatial Join.

Then create your SearchCursor like this:

addresses = r"c:\data.gdb\addresses"
census = r"c:\data.gdb\census"
fields = ["ADDRESS_ID", "RADIUS"]

with arcpy.da.SearchCursor(addresses, fields) as cursor:
    for row in cursor:

then for each row (= each point):

• Create an variable containing the ADDRESS_ID (ID = row[0]), i.e. the first field in your cursor, i.e. ADDRESS_ID)
• Buffer the point using radius as distance
• Select the underlying census polygon using Make Feature Layer + Select by Location
• Clip the buffer with the selected census polygon. The output is going to be the constraining feature class for the Create Random Points tool
• Create a random point in this zone with Create Random Points
• Add an ID field to the random point (same format as your ADDRESS_ID field from the address fc)
• Calculate the field, assign it the ID variable
• Clear the census selection.

You could either append each point to an empty point feature class you create before starting the cursor, or merge all points together when the cursor is done.
In order to make your script run faster, you should use whenever possible geometry objects instead of feature classes as inputs and outputs of the tool.
If you want to start learning Python, there is a free tutorial (3 hours) here. There are other trainings (not always free) and plenty of examples in the Online Help. Converting a ModelBuilder to a Python script sometimes help figuring out the correct syntax.

Good luck and don't hesitate to come back to me if you have questions,

Geraldine

Geraldine,
Thank you for your detailed response.  I will attempt this and see how far I can get.  Thank you also for directing me to the Python tutorial- that will be very helpful. 
Michelle