Add an entry about buffer and z coords
Resolves
@@ -5,7 +5,16 @@ Are there references for the algorithms used by shapely?
--------------------------------------------------------
Generally speaking, shapely's predicates and operations are derived from
-methods of the same name from the `JTS Topology Suite
-<https://locationtech.github.io/jts/>`__. See the JTS FAQ for `references
-describing the JTS algorithms
-<https://locationtech.github.io/jts/jts-faq.html#E1>`__.
+methods of the same name from GEOS_ and the `JTS Topology Suite`_. See the `JTS FAQ`_ for references
+describing the JTS algorithms.
+
+I used .buffer() on a geometry with Z coordinates. Where did the Z coordinates go?
+----------------------------------------------------------------------------------
+
+The buffer algorithm in GEOS_ is purely two-dimensional and discards any Z coordinates.
+This is generally the case for the GEOS algorithms.
+
+
+.. _GEOS: https://trac.osgeo.org/geos/
+.. _JTS Topology Suite: https://locationtech.github.io/jts/
+.. _JTS FAQ: https://locationtech.github.io/jts/jts-faq.html#E1
