Add contour on ggmap

Question

Firstly, this is my dataset.

Lon     Lat CPUE    Temperature
120.93  27  0.00    24.3
121.18  27  0.62    24.2
121.43  27  3.76    24.9
121.6   27.25   0.87    25
121.35  27.25   1.63    24.2
121.1   27.25   2.66    24.8
121.25  27.5    7.37    24.9
121.5   27.5    6.26    25.2
121.75  27.5    12.02   19.4
121.95  27.75   30.40   18.5
121.7   27.75   93.81   23.1
121.65  28  282.83  27.1
121.9   28  10.43   22.3
122.15  28  36.11   18.2
122.4   28.25   170.05  17.9
122.15  28.25   1170.97 18.8
122.3   28.5    0.00    18.4
122.55  28.5    149.99  17.6
122.8   28.75   118.27  18.5
122.55  28.75   1838.31 17.6
122.25  29  1218.93 21.2
122.5   29  1245.63 18.7
122.75  29  235.07  17.9 123    29  33.01   19.1

And this is my ggmap with CPUE data point:

I wonder if I can add temperature contour on this ggmap.

score 2 · Answer 1 · answered Sep 11 '17 at 16:09

Here's one approach, taking reference from this answer as there's insufficient data points in the dataframe to generate contour data:

# generate regular grid since geom_contour doesn't work on this dataset
temp <- akima::interp(df$Lon, df$Lat, df$Temperature)
df.expanded <- expand.grid(x = temp$x, y = temp$y)
df.expanded$z <- as.vector(temp$z)
df.expanded <- na.omit(df.expanded)
rm(temp)

library(ggplot2)

# plot contour using stat_contour() on expanded data frame
ggmap(background) +
  stat_contour(data = df.expanded, binwidth = 1,
               aes(x=x,y=y,z=z)) +
  geom_point(data = df, alpha = 0.5,
             aes(x = Lon, y = Lat, size = CPUE))

Data:

df <- read.table(header = T, text = "Lon     Lat CPUE    Temperature
120.93  27  0.00    24.3
                 121.18  27  0.62    24.2
                 121.43  27  3.76    24.9
                 121.6   27.25   0.87    25
                 121.35  27.25   1.63    24.2
                 121.1   27.25   2.66    24.8
                 121.25  27.5    7.37    24.9
                 121.5   27.5    6.26    25.2
                 121.75  27.5    12.02   19.4
                 121.95  27.75   30.40   18.5
                 121.7   27.75   93.81   23.1
                 121.65  28  282.83  27.1
                 121.9   28  10.43   22.3
                 122.15  28  36.11   18.2
                 122.4   28.25   170.05  17.9
                 122.15  28.25   1170.97 18.8
                 122.3   28.5    0.00    18.4
                 122.55  28.5    149.99  17.6
                 122.8   28.75   118.27  18.5
                 122.55  28.75   1838.31 17.6
                 122.25  29  1218.93 21.2
                 122.5   29  1245.63 18.7
                 122.75  29  235.07  17.9 123    29  33.01   19.1")

Background map data:

library(ggmap)
background <- get_map(location = c(min(df$Lon),
                                   min(df$Lat),
                                   max(df$Lon),
                                   max(df$Lat)),
                      zoom = 8)

Add contour on ggmap

1 Answers1