title: How to do kriging with polygon data? (Do not want block kriging)
body: <p>I am trying to apply kriging to interpolate the air pollution concentration (target variable)
  When I run the krige function as below, R return an error.</p>
  
  <p>RSPAVE is the target variable; 
  air is the dataset the contains the RSPAVE;
  TPU is the shapefile</p>
  
  <pre><code>k.o &lt;- krige(RSPAVE ~1, locations=air, newdata=TPU, model=m.RSPAVE.f)
  
  Error in predict.gstat(g, newdata = newdata, block = block, nsim = nsim, :
    gstat: value not allowed for: block kriging for long-lat data undefined
  </code></pre>
  
  <p>It is probably because my grid data is a shapefile. But I don't want block kriging, how can I turn the polygon to point, and apply ordinary kriging?</p>
  
  <p>Thank you very much!</p>