Hello. I do not know if you can merge polygons, but you can select easily:
> departements=map('france',namesonly=T) # returns a vector of names of regions
> map('france',regions=departements[1:20],namesonly=T) # use what you need with regions argument
Hope this helps,
At 16:29 18/11/2004, Michael Friendly wrote:
I'm doing some analyses of historical data from France in 1830 on 'moral statistics' that I'd like to
show on a map. I've done most of my analyses in SAS, but a few things would work better in R.
To do this, I have to adjust the modern map,
library(maps) map('france')
to adjust for changes in departments (86 in 1830, to 97 now). I've read the documentation
for the maps and maptools package, but there seems to be no functions to allow this, and
I can't find information on the exact structure of map datasets, but I understand them to
be delimited lists of polygon coordinates.
In SAS, all maps have (one or more) ID variables representing the geographical region,
and there is also a proc gremove that can remove internal boundaries inside the polygons
for regions with the same ID. Is there some way I can do this in R?
Here's what I did in SAS:
*-- Fix the map of France to conform to Guerry: - adjust the 97 current departments to correspond to the 86 in 1830 - delete those not part of France then ;
data gfrtemp; set maps.france; /* Corse was one dept - merge these to one area, new ID */ if id in (201, 202) then dept=200;
/* Seine et Oise (78) was cut into Essonne (91), Val d'Oise (95) and Yvelines (78) */ else if id in (91, 95) then dept=78;
/* Seine (75) now split into Hauts-de-Seine (92), Seine-Saint-Denis (93) et Val-de-Marne (94)*/ else if id in (92, 93, 94) then dept=75;
/* departments not part of France in 1830 */ else if id in ( 6, /* Alpes-Maritimes */ 73,74, /* Savoie, Haute-Savoie */ 90) /* Territore-de-Belfort */ then delete; else dept=id; run;
*-- remove internal boundaries based on merged DEPT; proc sort data=gfrtemp; by dept;
proc gremove data=gfrtemp out=gfrance; by dept; id id; run;
-- Michael Friendly Email: [EMAIL PROTECTED] Professor, Psychology Dept. York University Voice: 416 736-5115 x66249 Fax: 416 736-5814 4700 Keele Street http://www.math.yorku.ca/SCS/friendly.html Toronto, ONT M3J 1P3 CANADA
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St�phane DRAY
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