title: Convert normal latitude/longitude to Alber's Equal Area in R
body: <p>I have a data set, <code>dat</code>, in R with coordinates in WGS84. that looks like this (<code>dput</code> output below)</p>
  
  <pre><code>dat &lt;- structure(list(latitude = c(46.414597, 46.137664, 46.567187, 
  45.730901, 43.379185, 46.657572), longitude = c(-86.030373, -85.990492, 
  -87.954285, -87.674475, -86.226577, -89.807461), mat = c(5.21999979019165, 
  5.55999994277954, 4.03000020980835, 5.40000009536743, 8.3100004196167, 
  4.30000019073486), map = c(824.52001953125, 822.77001953125, 
  806.900024414062, 780.510009765625, 885.940002441406, 912.789978027344
  )), .Names = c("latitude", "longitude", "mat", "map"), row.names = c(NA, 
  -6L), class = c("data.table", "data.frame"), .internal.selfref = &lt;pointer: 0x10200fd78&gt;)
  
     latitude longitude  mat    map
  1: 46.41460 -86.03037 5.22 824.52
  2: 46.13766 -85.99049 5.56 822.77
  3: 46.56719 -87.95428 4.03 806.90
  4: 45.73090 -87.67448 5.40 780.51
  5: 43.37918 -86.22658 8.31 885.94
  6: 46.65757 -89.80746 4.30 912.79
  </code></pre>
  
  <p>I use the <code>sp</code> package to make this a spatial points data frame:</p>
  
  <pre><code>require(sp)
  dat.sp &lt;- SpatialPointsDataFrame(c(dat[,c('longitude','latitude')]), data = dat)
  </code></pre>
  
  <p>How can I convert these coordinates to the Alber's equal area projection?</p>