title: Whats the difference between z~1 and z~LON+LAT in plotting variogram in R?
body: <pre><code>library(sp)
  data(meuse)
  coordinates(meuse)&lt;-~x+y
  v&lt;-variogram(log(zinc)~1,meuse)
  v
           np       dist     gamma dir.hor dir.ver   id
      1   57   79.29244 0.1234479       0       0 var1
      2  299  163.97367 0.2162185       0       0 var1
      3  419  267.36483 0.3027859       0       0 var1
      4  457  372.73542 0.4121448       0       0 var1
      .
      .
  
  v1&lt;-variogram(log(zinc)~x+y,meuse)
  v1
              np       dist     gamma dir.hor dir.ver   id
          1   57   79.29244 0.1060834       0       0 var1
          2  299  163.97367 0.1829983       0       0 var1
          3  419  267.36483 0.2264256       0       0 var1
          4  457  372.73542 0.2847192       0       0 var1
          .
          .
  </code></pre>
  
  <p>From above following code and output I can found that <code>log(zinc)~1</code> and 
  <code>log(zinc)~x+y</code> returns the different gamma value for v and v1. What's the basic difference between these two operation?</p>
  
  <p><code>help(variogram)</code> told me that "formula defining the response vector and (possible) regressors, in case of absence of regressors, use e.g. z~1;".But,I didn't understand clearly these sentence! could anyone please tell me in details that when should I use <code>z~1</code> or when should I use <code>z~LON+LAT</code>?</p>