title: Variable marker size feature in leaflet R
body: <p>Is there a way to change the marker size in a map based on a certain value? </p>
  
  <p>For example, if I were plotting the population of individual cities and the marker was a circle, the circle would be bigger for the more populated cities.</p>
  
  <p>I was wondering if there was a specific feature for this or if I could add a column to the dataset which has the individual marker sizes for each lat/lon I want to plot. </p>
  
  <p>Thanks!</p>