utility - How many sites are near the blocks (site density near residents)
Source:R/getblocks_diagnostics.R
      getblocks_summarize_sites_per_block.Rdutility - How many sites are near the blocks (site density near residents)
Arguments
- x
 The output of
getblocksnearby()like testoutput_getblocksnearby_10pts_1miles- varname
 colname of variable in data.table x that is the one to summarize by