On Tue, 21 Apr 2009, Alina Sheyman wrote:
To rephrase my question and explain my problem further
I have already created a map for revenue by zip code, in the state of
Massachusetts. To accomplish that I used a shapefile for Massachusetts and a
dataframe with my revenue/zip codes.
What I am trying to do now is to have the same map done not by zip code, but
rather by districts, as defined by zip codes.
Basically what I've done was to introduce a new variable "district" into my
dataset along with a zip code. At the same time my basic state map (by zip)
still comes from a shape file and I can't introduce a new variable into the
shape file.
Does anyone know if there's any way I can accomplish what I'm trying to
do or do I basically need to create a new shapefile with districts already
in the file?
OK, that wasn't too clear before. Look at unionSpatialPolygons() in
maptools - it will take a vector of districts matching all your zip codes,
and join together the geometries belonging to each district, dropping
internal boundaries. The district IDs become the Polygons object IDs.
There is no data frame in the object, because it isn't obvious how you
might want to aggregate it.
Hope this helps,
Roger
On Mon, Apr 20, 2009 at 5:53 PM, Don MacQueen <m...@llnl.gov> wrote:
This is a pretty general question, and there are potentially many ways to
do it.
One way to get started would be to follow the example(s) in the help page
for the overlay() function in the sp package.
-Don
At 1:26 PM -0400 4/20/09, Alina Sheyman wrote:
I have a list of made-up districts and corresponding zip codes. Based on
that I want to define my own polygons (for each district) and then use
them
to create a map. Does anyone know how I would go about defining these?
thank you
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Don MacQueen
Environmental Protection Department
Lawrence Livermore National Laboratory
Livermore, CA, USA
925-423-1062
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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.biv...@nhh.no
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