span class='no'>flow</span>, <span class='no'>zones</span>, <span class='no'>aggzones</span>, <span class='kw'>aggzone_points</span> <span class='kw'>=</span> <span class='kw'>NULL</span>,
  <span class='kw'>cols</span> <span class='kw'>=</span> <span class='fl'>FALSE</span>, <span class='kw'>aggcols</span> <span class='kw'>=</span> <span class='fl'>FALSE</span>, <span class='kw'>FUN</span> <span class='kw'>=</span> <span class='no'>sum</span>,
  <span class='kw'>prop_by_area</span> <span class='kw'>=</span