mkaravel commented on PR #13227:
URL: https://github.com/apache/iceberg/pull/13227#issuecomment-2942186507

   @jiayuasu Thank you for driving this!
   
   I am not able to comment directly at appropriate place since there are no 
changes there, which is why I writing this as a high level comment in the PR.
   
   In line 684 of the existing spec (prior to this PR) we state:
   > For `geometry` and `geography` types, `lower_bounds` and `upper_bounds` 
are both points of the following coordinates X, Y, Z, and M (see [Appendix 
G](#appendix-g-geospatial-notes)) which are the lower / upper bound of all 
objects in the file. For the X values only, xmin may be greater than xmax, in 
which case an object in this bounding box may match if it contains an X such 
that `x >= xmin` OR`x <= xmax`. In geographic terminology, the concepts of 
`xmin`, `xmax`, `ymin`, and `ymax` are also known as `westernmost`, 
`easternmost`, `southernmost` and `northernmost`, respectively. For `geography` 
types, these points are further restricted to the canonical ranges of [-180 
180] for X and [-90 90] for Y.
   
   I believe that in order to make the spec self-consistent it would make sense 
to rephrase this and specify that `xmin` can be greater than `xmax` for 
geographies only.
   
   How about the following slight modification?
   > For `geometry` and `geography` types, `lower_bounds` and `upper_bounds` 
are both points of the following coordinates X, Y, Z, and M (see [Appendix 
G](https://github.com/apache/iceberg/blob/47e15e566868c96420667bb291835f2c470f678d/format/spec.md#appendix-g-geospatial-notes))
 which are the lower / upper bound of all objects in the file.
   >
   > For `geography`, for the X values only, `xmin` may be greater than `xmax`, 
in which case an object in this bounding box may match if it contains an X such 
that `x >= xmin` OR `x <= xmax`. In geographic terminology, the concepts of 
`xmin`, `xmax`, `ymin`, and `ymax` are also known as `westernmost`, 
`easternmost`, `southernmost` and `northernmost`, respectively. These points 
are further restricted to the canonical ranges of [-180..180] for X and 
[-90..90] for Y.


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