Optional column metadata field to store bounding box information (#21)

Co-authored-by: Brendan Ward <[email protected]>

Author: jorisvandenbossche

format-specs/geoparquet.md

@@ -52,6 +52,7 @@ Each geometry column in the dataset must be included in the columns field above
 | ---------- | ----------------------------------------------------------------------- | ------------------------------------------------------------------------------------------------------------------------------------------------- |
 | crs       | string   | **REQUIRED** [WKT2](http://docs.opengeospatial.org/is/12-063r5/12-063r5.html) string representing the Coordinate Reference System (CRS) of the geometry.  |
 | encoding | string | **REQUIRED** Name of the geometry encoding format. Currently only 'WKB' is supported. |
+| bbox   | \[number] | **OPTIONAL** Bounding Box of the geometries in the file, formatted according to [RFC 7946, section 5](https://tools.ietf.org/html/rfc7946#section-5) |
 
 #### crs
 
@@ -78,6 +79,16 @@ This is the binary format that the geometry is encoded in. The string 'WKB' to r
 [Well Known Binary](https://en.wikipedia.org/wiki/Well-known_text_representation_of_geometry#Well-known_binary) is the only current option, but future versions
 of the spec may support alternative encodings. This should be the ["standard"](https://libgeos.org/specifications/wkb/#standard-wkb) WKB representation.
 
+#### bbox
+
+Bounding boxes are used to help define the spatial extent of each geometry column.
+Implementations of this schema may choose to use those bounding boxes to filter
+partitions (files) of a partitioned dataset.
+
+The bbox, if specified, must be encoded with an array containing the minimum
+and maximum values of each dimension: `[<xmin>, <ymin>, <xmax>, <ymax>]`.
+This follows the GeoJSON specification ([RFC 7946, section 5](https://tools.ietf.org/html/rfc7946#section-5)).
+
 ### Additional information
 
 ## TODO