[R-sig-Geo] plotting geographic coordinates on a map

Robert Hijmans r.hijmans at gmail.com
Fri Jul 15 02:29:34 CEST 2011

> I simply would like to plot these on a map of the US. I've tried all sorts
of approaches, including 
>> map('usa', project='albers', par=c(39,34)) 
>> points(x=data$LONGITUDE, y=data$LATITUTUDE, col='red') 

You are plotting longitude/latitude data on an map with Albers projection.
Won't give you what you want. 
Either transform the long/lat data to Albers (with the right parameters),
e.g. using spTransform (rgdal package), or do:

points(x=data$LONGITUDE, y=data$LATITUTUDE, col='red') 

#You can have a look at the difference in coordinates like this
locator(1) # click on the center of the map
map('usa', project='albers') 
locator(1) # click on the center of the map

>> library(sp) 
>> coordinates(WNV) <- c("latitude", "longitude") 
>> map('world') 
>> plot(WNV$latitude, WNV$longitude) 

Instead, do:

plot(WNV, add=TRUE) 

Hth, Robert

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