Hi. I have a requirement to plot a series of points on a map of Canada along
with boundaries defining search and rescue (SAR) regions. I have been
successful in plotting the map of Canada (Lambert projection) and the points,
but I have been unable thus far to plot the SAR regions on top of the map. I'm
at the point now where I need help to resolve the issue.
To plot the map of Canada, I have used the following line of code:
map(database= "worldHires","Canada", ylim=c(39,90), xlim=c(-150,-25),
col=alpha("grey90",0.5), fill=TRUE, projection="lambert", param=c(50,65))
Note that the ylim and xlim limits go wider that the actual coordinates of
Canada, but that is necessary because the SAR regions go out to sea quite a
distance. Also, I need the map to go all the way to the North Pole.
To plot the points, I have used a "dummy" list of points which I will
eventually replace with my real data. I convert the points to the lambert
projection on the fly using the following lines of code:
lon <- c(-60, -60, -80, -80.1, -90, -105, -140) #a test longitude vector
lat <- c(42.5, 42.6, 54.6, 54.4, 75, 68.3, 60) #a test latitude vector
coord <- mapproject(lon, lat, proj="lambert", param=c(50,65)) #convert
points to projected lat/long
points(coord, add=TRUE, pch=20, cex=1.2, col=alpha("red", 0.5)) #plot
converted points
As stated, plotting the SAR regions has not worked thus far. The best I have
ever gotten is a square box around the map. I have data files that list the
coordinates of the SAR regions, which is a succession of up to 12100 lat & long
points. A colleague converted those data files into shapefiles defining
polygons, with the coordinates already projected to Lambert. I have tried
various options to plot the regions, but none have worked.
Using readOGR:
region <- readOGR(dsn="C:/myRfolder",layer="mySARshapefile")
plot(region, add=TRUE, xlim=c(-150,-25),ylim=c(39,90),
col=alpha("lightgreen", 0.6), border=TRUE)
Using read.shp and draw.shp:
region <- read.shp("C:/myRfolder/mySARshapefile.shp")
draw.shape(shape=region, type="poly", col="red")
Using readShapePoly:
region <- readShapePoly("C:/ myRfolder/mySARshapefile.shp")
plot(halRegion, add=TRUE, xlim=c(-150,-25),ylim=c(39,90),
col=alpha("lightgreen", 0.6), border=TRUE)
Using readShapeLines after converting the region coordinates to a Lines
shapefile instead of a Polygon shapefile:
region <- readShapeLines("C:/myRfolder/mySARshapefile_lines.shp")
lines(region, col=alpha("black", 0.6))
I have tried playing with spplot, but I haven't quite understood how this one
works yet (gives me an error message: "Error in
stack.SpatialPointsDataFrame(as(data, "SpatialPointsDataFrame"), : all
factors should have identical levels")
I would appreciate any help or insight that you could provide to help me get
those boundaries drawn on-top of the country map.
Thanks
Alain Dubreuil
Ottawa, Canada
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