Geo-shapes use a completely different approach than geo-points. A circle on a computer screen does not consist of a perfect continuous line. Instead it is drawn by coloring adjacent pixels as an approximation of a circle. Geo-shapes work in much the same way.
Complex shapes—such as points, lines, polygons, multipolygons, and polygons with holes,--are “painted” onto a grid of geohash cells, and the shape is converted into a list of the geohashes of all the cells that it touches.
Actually, two types of grids can be used with geo-shapes: geohashes, which we have already discussed and which are the default encoding, and quad trees. Quad trees are similar to geohashes except that there are only four cells at each level, instead of 32. The difference comes down to a choice of encoding.
All of the geohashes that compose a shape are indexed as if they were terms. With this information in the index, it is easy to determine whether one shape intersects with another, as they will share the same geohash terms.
That is the extent of what you can do with geo-shapes: determine the
relationship between a query shape and a shape in the index. The
can be one of the following:
- The query shape overlaps with the indexed shape (default).
- The query shape does not overlap at all with the indexed shape.
- The indexed shape is entirely within the query shape.
Geo-shapes cannot be used to caculate distance, cannot be used for sorting or scoring, and cannot be used in aggregations.