title: R plot transparent coloured points
body: <p>I am currently plotting some points onto an existing map of the UK using the following:</p>
  
  <p>points(X$Long, X$Lat, col=X$Col, pch=16,cex=X$Size)</p>
  
  <p>X is the data frame.</p>
  
  <p>The colour of the points varies along with the size.(yellow to orange to red)</p>
  
  <p>I would like the points to be semi transparent so that you can still just about see the lines underneath the points.</p>
  
  <p>What is the easiest way to do this I have already seen some code to alter the colour code but is there an easier way?</p>
  
  <p>Thank you in advance.</p>