code: func (geoIndex *geoIndex) AddEntryAt(point Point) interface{} {
  	square := cellOf(point, geoIndex.resolution)
  
  	if _, ok := geoIndex.index[square]; !ok {
  		geoIndex.index[square] = geoIndex.newEntry()
  	}
  
  	return geoIndex.index[square]
  }
docs: // AddEntryAt adds an entry if missing, returns the entry at specific position.