Can a new point automatically be populated with data from the containing polygon

Question

I need some help to create a script.

Imagine that I'm using 3 shapes: 1 point and 2 polygons. When I create a new point I want it to assume some attributes of the polygons in which that point is inserted.

Any idea?

Answer 1

Loop through your points (search cursor), then loop though you polygons (search cursor). Once you find the point is in the polygon (polygon.contains(point), then as you are already in the record of the polygon and point, just update by setting the attribute in the point, equal to the attribute you require from the polygon. simply then update the row in the point table, exit the polygon loop, then load the next point, etc.

If you can wait until monday, I can write some arcpy for you; it's very, very easy and I think I did the very same thing last week.

fcPnt = "C:\\Path\\to\\Point\\Data.sde\\PointDS"
fcPoly = "C:\\Path\\To\\Polygon\\Data.sde\\PolygonDS"
sSQL "Sql to sub select data for your points if you need to

pntcur = arcpy.UpdateCursor(fcPnt, sSQL)
# can also be pntcur = arcpy.SearchCursor(fcPnt) to select all points
for row in pntcur:
    #if you have access to the point x and y through column data, then use:
    geom = arcpy.Point(row.X,row.Y)
    #otherwise cast the shape to an arcpy point
    #geom = arcpy.Point(row.shape.extent.XMax,row.shape.extent.YMax)
    # or geom = arcpy.Point(row.GetPart()) as we know it is a point object, we dont need to reference the part number
    polycurs = arcpy.SearchCursor(fcPoly)
    for polyRow in polycurs:
        poly = polyRow.Shape
        if poly.contains(geom):
            row.SomeRow = polyRow.SomePolyRowData
            row.SomeOtherRow = polyRow.SomeOtherPolyRowData
            ...
            ...
        del polyRow
        del poly

    del polycurs
    pntcur.updateRow(row)
    del row

del pntcur

Or there, or there abouts!

Answer 2

What you're trying to do is called a "point in polygon" search.

Python

I'm guessing you're trying to script it using python given your tag. A google search for python "point in polygon" should give you a good start. A top result I get is this page which looks like it may be adaptable to do what you want: http://www.heikkitoivonen.net/blog/2009/01/26/point-in-polygon-in-python/

Spatial Database

Alternately you can offload the processing to a spatial database, i.e. spatialLite. You store your polygons in there and then when a new point is created you use some SQL to get the attributes for whichever polygons its within. https://code.google.com/p/xenia/wiki/SpatialLite - has a little more information

Python Libaries There are also some python GIS libraries out there which could allow you to offload it to them rather than roll your own. Unfortunately I don't know any of their names. :-S

Answer 3

I'm not sure that that is possible, or the best way to approach the problem. I would imagine a better way is to create all the points first, or load them into your GIS somehow, and then update the desired fields in the points shape based on which polygon they are in, which is very possible in most GIS software, including open-source.

State the software you intend to you use if you need more pointers.

Answer 4

How about:

1. Select by location -> point(s) contained by polygon.
2. SearchCursor(polygonFeatureClass) -> store values of attributes in
3. variables Insert/UpdateCursor(pointFeatureClass) -> update attribute with stored values

Answer 5

In ArcGIS you can simply use Spatial Join or Identity (ArcInfo only) to join attributes from one layer to another. Both tools will create new point layer.

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If you don't want create new layer and have greater control on selection method, here's the script similar to @Hairy's script but uses Feature Layers and Select By Location:

import arcpy
arcpy.env.overwriteOutput = True

#adapt the following variabled to your data:
polygonLayer = r"C:\tmp\Test.gdb\Polygons"
pointLayer = r"C:\tmp\Test.gdb\Points"
copyField = "FieldNameToCopy"


#add new field to target feature class if it don't exists (you can delete it if you plan to create field manually)
fieldList = arcpy.ListFields(pointLayer)
fieldNameList = []
for field in fieldList:
    fieldNameList.append(field.name)
fieldType = arcpy.ListFields(polygonLayer,copyField)[0].type
if not copyField in fieldNameList:
    arcpy.AddField_management(pointLayer, copyField, fieldType)

arcpy.MakeFeatureLayer_management(polygonLayer, "PolygonLayer")

pntCursor = arcpy.UpdateCursor(pointLayer)
for pnt in pntCursor:
    rowID = pnt.OBJECTID
    arcpy.MakeFeatureLayer_management(pointLayer, "PointLayer", '"OBJECTID" = ' + str(rowID))

    #polygon selection based on CONTAINS selection method
    arcpy.SelectLayerByLocation_management("PolygonLayer", "CONTAINS", "PointLayer")

    #copy field values from polygon to point layer    
    polyCursor = arcpy.SearchCursor("PolygonLayer")        
    for poly in polyCursor:
        pnt.setValue(copyField, poly.getValue(copyField))
        pntCursor.updateRow(pnt)

    arcpy.Delete_management("PointLayer")        

del pntCursor, polyCursor, pnt, poly