title: Determining the distance between two ZIP codes (alternatives to mapdist)
body: <p>I want to calculate the distance between approx. 100,000 different ZIP codes. I know about the <code>mapdist</code> function in the <code>ggmap</code> package</p>
  
  <p><code>mapdist</code> works perfectly:</p>
  
  <pre><code>library(ggmap)
  mapdist('Washington', 'New York', mode = 'driving')
  
  #         from       to      m      km    miles seconds  minutes    hours
  # 1 Washington New York 366284 366.284 227.6089   13997 233.2833 3.888056
  
  
  mapdist('20001', '10001', mode = 'driving')
  
  #    from    to      m      km    miles seconds minutes    hours
  # 1 20001 10001 363119 363.119 225.6421   13713  228.55 3.809167
  </code></pre>
  
  <p>However, <code>mapdist</code> relies on the Google Geocoding API which is subject to a <strong>query limit of 2,500 geolocation requests</strong> per day.</p>
  
  <p>Are you aware of any alternative r code to calculate the distance between two points using another service which has a higher request limit (such as Nokia Maps or Bing)?</p>