Question

I have plotted a contour map but i need to make some improvements. This is the structure of the data that are used:

str(lon_sst)
# num [1:360(1d)] -179.5 -178.5 -177.5 -176.5 -175.5 ...

str(lat_sst)
# num [1:180(1d)] -89.5 -88.5 -87.5 -86.5 -85.5 -84.5 -83.5 -82.5 -81.5 -80.5 ...

dim(cor_Houlgrave_SF_SST_JJA_try)
# [1] 360 180

require(maps)
maps::map(database="world", fill=TRUE, col="light blue")
maps::map.axes()
contour(x=lon_sst, y=lat_sst, z=cor_Houlgrave_SF_SST_JJA_try[c(181:360, 1:180),],
        zlim=c(-1,1), add=TRUE)
par(ask=TRUE)
filled.contour(x = lon_sst, y=lat_sst,
               z=cor_Houlgrave_SF_SST_JJA_try[c(181:360, 1:180),],
               zlim=c(-1,1), color.palette=heat.colors)

Because most of the correlations are close to 0, it is very hard to see the big ones.

1. Can i make it easier to see, or can i change the resolution so i can zoom it in? At the moment the contours are too tightly spaced so I can’t see what the contour levels were.

2. Where can i see the increment, i set my range as (-1,1), i don’t know how to set the interval manually.

3. Can someone tell me how to plot a specific region of the map, like longitude from 100 to 160 and latitude from -50 to -80? I have tried to replace lon_sst and lat_sst, but it has a dimension error. Thanks.

Answer 1

To answer 1 and 3 which appear to be the same request, try:

maps::map(database="world", fill=TRUE, col="light blue", 
                            ylim=c(-80, -50), xlim=c(100,160) )

To address 2: You have a much smaller range than [-1,1]. The labels on those contour lines are numbers like .06, -.02 and .02. The contour function will accept either an ‘nlevels’ or a ‘levels’ argument. Once you have a blown up section you can use that to adjust the z-resolution of contours.