Once {HEAD ~ the minimum number} of index entries is determined a grid can be partitioned into {TAIL ~ the appropriate number} of grid cells to support efficient grid indexing 
Once { HEAD ~ the minimum number } of index entries is determined a grid can be partitioned into { TAIL ~ the appropriate number } of grid cells to support efficient grid indexing
OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH