help with contour plot

[jatin.kala.jk]

Hi ggplot community,
I am trying to do a contour plot of (longitude, latitude, concentration).
This is easy enough using filled.contour.
However, i am trying to do the same contour plot using ggplot, and overlaying the plot on google-map.
The script and data being read is attached.
 test_filled_contour_plot.png is what contour.filled gives me.
GF_test.png is the output from using ggplot. Something is going wrong, but i can't figure out what, and it's doing my head-in....
Any help would be greatly appreciated.
Cheers,
Jatin

[Ista Zahn]

Hi Jatin,

My basic approach would be

load("ALL_HOURLY_NOX_Processed")

data_plot <- max_conc
dimnames(data_plot) <- list(lon = lon, lat = lat)

data_plot <- reshape2::melt(data_plot, value.name = "max_conc")

ggplot(data_plot, aes(lon, lat, color = max_conc, z = max_conc)) +
stat_contour(aes(color = ..level.., fill = ..level..), geom =
"contour", bins = 10)

But here we hit a dead end, because stat_contour doesn't generate
lines that work with geom_polygon, and we need geom_polygon for fill.

ggplot(data_plot, aes(lon, lat, color = max_conc, z = max_conc)) +
stat_contour(aes(color = ..level.., fill = ..level..), geom =
"polygon", bins = 10)

is tantalizingly close, but not good enough. Making it work correctly
will be hard I'm afraid. See
https://github.com/tidyverse/ggplot2/issues/1066 and despair.

Something along the lines of

ggplot(data_plot, aes(lon, lat, z = max_conc)) +
geom_raster(aes(fill = max_conc)) +
geom_contour(bins = 10)

might be good enough.

Best,
Ista

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