Basic Iterators
The DGGS SDK provides basic operations to traverse cell locations:
 Move  Given a cell index, return the next cell in a given direction where the definition of direction is based on the tile structure and indexing;
 Neighbors  Given a cell index, return all neighbor cells (touch);
 Parent & Children  Given a cell index, return set of all child cells at the next refinement and its single parent cell;
 Natural Tile: Given a cell index and a depth, return set of all child cells and refinements to the given depth;
 Cover  Given a cell index and a depth, return all the congruent cells at the given depth.
Selection Iterators
Basic iterators can be used to build selection iterators that run over cell collections independent of indexing:
 Feature Geometry  Given a feature geometry and a cell resolution, return all cells that intersect the geometry at the given resolution;
 Condition  Given a cell resolution and a condition, return all cells that contain data values that meet the given condition;
 Conditional Flood Fill  Given a cell index and a condition, return all touching cells of the same resolution that contain data values that meet the given condition;
 Shortest Path  Given 2 cell indices and cost function, return the set of cells of the same resolution that represent the shortest path.
