[R-sig-Geo] Detect islands (of more than 1 areas or polygons) into a cartography

[Marc Marí Dell'Olmo]

n.comp.nb() function is exactly what I need. Thank you very much!

Marc

2012/1/2 Roger Bivand <Roger.Bivand at nhh.no>:
> On Fri, 30 Dec 2011, Marc Marí Dell'Olmo wrote:
>
>> Dear all,
>>
>> Anyone knows a function to detect if there are islands into a
>> cartography. I refer to islands with more than one area (or polygons).
>> In other words, I would like to detect how many connected components I
>> have in the graph.
>>
>> On the other hand, I would like to know the “id” of the areas (or
>> polygons) for each island.
>>
>
> This wasn't easy to grasp. By graph, do you mean the neighbour graph of the
> Polygons objects in a SpatialPolygons object? Could you use the North
> Carolina counties data set included in maptools to give an example of your
> question? You'll find additional information in spdep, see the poly2nb() and
> n.comp.nb() functions.
>
> Roger
>
>> Note: I usually use the "readShapePoly " to open the cartography.
>>
>> Thank you very much!
>> Marc
>>
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>
> --
> Roger Bivand
> Department of Economics, NHH Norwegian School of Economics,
> 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