title: R plot filled.contour() output in ggpplot2
body: <p>I want to plot this figure created with filled.contour(), but in ggplot2, how do I do this? </p>
  
  <p>I want to use ggplot2 because the graphing conventions are easier. The reason I want to use filled.contour() is because I tried geom_tile() and image.plot() and they both created very tile like outputs, and I need an output similar to filled.contour(). </p>
  
  <p>This is my figure:</p>
  
  <p><img src="https://i.stack.imgur.com/cJ6HY.jpg" alt="enter image description here"></p>
  
  <p>Code:</p>
  
  <pre class="lang-r prettyprint-override"><code>library(akima)
  
  df &lt;-read.table("Petra_phytoplankton+POM_xydata_minusNAs_noduplicates.txt",header=T)
  attach(df)
  names(df)
  fld &lt;- with(df, interp(x = longitude, y = latitude, z = d13C))
  
  filled.contour.ungeoreferenced &lt;- 
    (filled.contour(x = fld$x,
                    y = fld$y,
                    z = fld$z,
                    color.palette =
                      colorRampPalette(c("blue", "green", "yellow",
                                         "orange", "red")),
                    xlab = "Longitude",
                    ylab = "Latitude",
                    key.title = title(main = "d13C", 
                                      cex.main = 1)))
  </code></pre>
  
  <p>Snippet of data:</p>
  
  <pre class="lang-r prettyprint-override"><code>latitude    longitude   d13C
  -65 -70 -27.7
  -61 150 -32.2
  -61 150 -28.3
  -60 116 -26.8
  -60 116 -24.7
  -47 38  -24.8
  -38 150 -20.5
  19  -65.7   -19.9
  19  -65.5   -18.5
  18  -60.7   -20
  18  -58.5   -18.2
  18  -57.8   -19
  17  -55.4   -18.6
  17  -50.8   -18
  17  -47.1   -18.3
  17  -45.5   -19.4
  16  -43.3   -17.9
  15  -40.7   -18.5
  14  -39.3   -19.9
  12  -36.7   -19.9
  12  -36.2   -19.9
  11  -34.4   -19.2
  10  -32 -18.5
  9   -30.3   -19.3
  8   -29.2   -19.4
  7   -26.6   -18.2
  7   -25.5   -19.3
  6   23.9    -20
  3   -21.3   -20.4
  </code></pre>