[R-sig-Geo] Merging two spatial polygon objects

[Roger Bivand]

On Thu, 5 Nov 2009, Roger Bivand wrote:

> On Thu, 5 Nov 2009, BRWIN338 at aol.com wrote:
>
>> Good Evening
>> 
>> I have two spatial polygon objects. The first  "StMaps50"  contains state
>> level map data for the 50 US states.  The second  "CAMaps" contains
>> provincial and territorial polygons  for Canada.  I would like to merge 
>> these two
>> objects into a  single Canada-US spatial polygon object that I could then 
>> write
>> to a  shapefile.  The data fields in the @data component have been
>> constructed  with identical fields.  I have tried using the  maptools 
>> "spRbind"
>> function but get the following error  message:
>
> With recent versions of sp, you can say:
>
> rownames(StMaps50)
> rownames(CAMaps)

Sorry, on checking:

row.names(StMaps50)
row.names(CAMaps)

(rownames() is a method for matrices, row.names() for data.frames and 
friends).

Roger

>
> By default, the IDs for each Polygons object, corresponding to each row in 
> the data.frame object in the "data" slot, are the feature IDs read in form 
> file. In the case of shapefiles, these usually run from "0" to say n-1. So 
> they will be the same. Use the spChFIDs() method in maptools to change the 
> IDs of at least one of your objects to disambiguate them (say paste "US" in 
> front of the US ones and "CAN" in front of the Canadian ones). I'm also 
> assuming the the coordinate reference systems are identical.
>
> Hope this helps,
>
> Roger
>
>> 
>>> spRbind(StMaps50,CAMaps)
>> Error in spRbind(as(obj,  "SpatialPolygons"), as(x, "SpatialPolygons")) :
>> non-unique polygon  IDs
>> 
>> I have attached additional information below.
>> Any suggestions would be appreciated.
>> 
>> Joe
>> 
>> ##################################################
>>>  class(StMaps50)
>> [1] "SpatialPolygonsDataFrame"
>> attr(,"package")
>> [1]  "sp"
>> 
>>> _StMaps50 at data[1:5_ (mailto:StMaps50 at data[1:5) ,]
>> ctry        sname sabbr sfips  pfips
>> 1   US   Washington     WA    53    NA
>> 2    US      Montana    MT     30    NA
>> 3    US        Maine     ME    23    NA
>> 4   US North  Dakota    ND    38     NA
>> 5   US South Dakota    SD     46    NA
>> 
>>> class(CAMaps)
>> [1]  "SpatialPolygonsDataFrame"
>> attr(,"package")
>> [1] "sp"
>> 
>>> _CAMaps at data_ (mailto:CAMaps at data)
>> ctry                  sname sabbr sfips pfips
>> 0     CA                Alberta   ALB    61  CA01
>> 1     CA      British Columbia    BCL    62  CA02
>> 2     CA               Manitoba   MNT    63  CA03
>> 3     CA         New Brunswick    NBR    64  CA04
>> 4     CA           Nova  Scotia   NSC    65  CA07
>> 5    CA  Northwest Territories   NTR    66   CA06
>> 6     CA           Newfoundland   NWF    67   CA05
>> 7     CA                Ontario   ONT    68  CA08
>> 8     CA  Prince Edward Island   PEI    69   CA09
>> 9     CA                 Quebec   QUE    70  CA10
>> 10    CA           Saskatchewan   SSK    71  CA11
>> 11    CA       Yukon Territory    YTR    72  CA12
>>> 
>> ################################################
>> 
>>
>> 	[[alternative HTML version deleted]]
>> 
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>> 
>
>

-- 
Roger Bivand
Economic Geography Section, Department of Economics, Norwegian School of
Economics and Business Administration, Helleveien 30, N-5045 Bergen,
Norway. voice: +47 55 95 93 55; fax +47 55 95 95 43
e-mail: Roger.Bivand at nhh.no