title: Change plotting order of categories of data in tmap map R
body: <p>I am plotting some spatial data in R using the <code>tmap</code> package. I define breaks and plot color in the <code>tm_dots</code> function. I'd like to be able to define the plot order of the categories so that they are defined by the category (highest category on top, second highest below that, etc.). I need to be able to see clearly where the highest category points are. I know this could be achieved with multiple spatial point data frames, but is there another less clunky way? Below is an example using the meuse data. I make the points huge so they overlap. So ideally here in the plot the plot order would be: blue, green, orange, red.</p>
  
  <pre><code>libary(tmap)
  library(sp)
  
  data("meuse")
  
  coordinates(meuse) &lt;- c("x","y")
  
  tm_layout() +
    tm_shape(meuse) + tm_dots("cadmium", breaks = c(1,2,3,4,Inf), palette = "-Spectral", auto.palette.mapping = FALSE,
                              size = 1) + 
    tm_legend(legend.outside = TRUE)
  </code></pre>
  
  <p><a href="https://i.stack.imgur.com/pT1tr.png" rel="noreferrer"><img src="https://i.stack.imgur.com/pT1tr.png" alt="enter image description here"></a></p>