title: Plotting points on a map with size depending on category count
body: <p>I have a dataset with animal trappings, where in each location I have multiple animals of several different species captured. I would like to plot this information on a map, such that each point would represent location of trapping of a given species and the size of each point would represent a number of animals of this species trapped in this location. I can do all this except the last point, differentiating point size depending on the counts in each category and location. </p>
  
  <p>Data:</p>
  
  <pre><code>&gt; test
  Species  Location      Long      Lat
  1  Species1 Location4 13.179328 32.83438
  2  Species1 Location4 13.179328 32.83438
  3  Species1 Location4 13.179328 32.83438
  4  Species1 Location4 13.179328 32.83438
  5  Species1 Location4 13.179328 32.83438
  6  Species1 Location4 13.179328 32.83438
  7  Species1 Location4 13.179328 32.83438
  8  Species1 Location4 13.179328 32.83438
  9  Species1 Location4 13.179328 32.83438
  10 Species1 Location4 13.179328 32.83438
  11 Species1 Location4 13.179328 32.83438
  12 Species1 Location4 13.179328 32.83438
  13 Species1 Location4 13.179328 32.83438
  14 Species1 Location4 13.179328 32.83438
  15 Species1 Location2 13.857541 32.71680
  16 Species1 Location2 13.857541 32.71680
  17 Species1 Location2 13.857541 32.71680
  18 Species1 Location1  7.584970 33.77976
  19 Species1 Location1  7.564263 33.81079
  20 Species1 Location1  7.555380 33.79994
  21 Species2 Location1  7.542248 33.79943
  22 Species2 Location1  7.562118 33.79340
  23 Species2 Location1  7.542248 33.79943
  24 Species2 Location1  7.555380 33.79994
  25 Species2 Location1  7.542248 33.79943
  26 Species2 Location3 11.377850 33.20891
  27 Species2 Location3 11.377850 33.20891
  28 Species2 Location3 11.377850 33.20891
  29 Species2 Location3 11.377850 33.20891
  30 Species2 Location3 11.377850 33.20891
  31 Species1 Location2 13.834581 32.72319
  32 Species1 Location2 13.834581 32.72319
  33 Species1 Location2 13.834581 32.72319
  34 Species1 Location2 13.834581 32.72319
  35 Species1 Location2 13.834581 32.72319
  36 Species1 Location2 13.834581 32.72319
  37 Species1 Location2 13.834581 32.72319
  38 Species1 Location2 13.834581 32.72319
  39 Species1 Location2 13.834581 32.72319
  40 Species1 Location2 13.834581 32.72319
  41 Species1 Location2 13.834581 32.72319
  42 Species1 Location2 13.834581 32.72319
  43 Species1 Location2 13.834581 32.72319
  44 Species1 Location2 13.834581 32.72319
  45 Species1 Location2 13.834581 32.72319
  46 Species1 Location2 13.834581 32.72319
  47 Species1 Location2 13.834581 32.72319
  48 Species1 Location2 13.834581 32.72319
  49 Species1 Location2 13.834581 32.72319
  50 Species1 Location2 13.834581 32.72319
  
  &gt; tapply(test$Species,test$Location,length)
  Location1 Location2 Location3 Location4 
          8        23         5        14 
  </code></pre>
  
  <p>Standard ggmap plot:</p>
  
  <pre><code>m&lt;-get_map(location=c(lon=10.6858397, lat=32.7996318), zoom=7, color="bw")
  
  ggmap(m, extent = "normal") +
    geom_point(aes(x = Long, y = Lat, colour = Species, size = 2), data = test)
  </code></pre>
  
  <p><a href="https://i.stack.imgur.com/bfwNK.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/bfwNK.png" alt="Trapping locations on a map"></a></p>
  
  <p>How do I now change the size of the point depending on how many animals of each species were captured in a location?</p>