Merge pull request #305 from Deltares/chore/222-investigate-igraph-pe…

…rformance

chore: #222 investigate igraph performance

.gitignore

@@ -83,6 +83,7 @@ instance/
 
 # Sphinx documentation
 docs/_build/
+docs/_examples/
 
 # PyBuilder
 target/

docs/collaboration/implementation_decisions.rst

@@ -11,4 +11,31 @@ We tried replacing `geopy <https://geopy.readthedocs.io/en/stable/>`_ with simil
 However, this did not seem to be a valid alternative as the accuracy and simplicity of geopy outweights the benefit of replacing it with similar extensive logic as can be seen in this `example <https://autogis-site.readthedocs.io/en/2019/notebooks/L2/calculating-distances.html>`_. 
 
 .. tip:: 
-    This topic was handled in issue `188 <https://github.com/Deltares/ra2ce/issues/188>`_
+    This topic was handled in issue `188 <https://github.com/Deltares/ra2ce/issues/188>`_
+
+Replacing NetworkX with igraph
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+Currently NetworkX is used as graph framework `NetworkX <https://networkx.org/>`_.
+A downside of this framework is the known poor performance.
+For this reason igraph `igraph <https://igraph.org/python/>`_ has been assessed as possible replacement of NetworkX.
+
+.. tip:: 
+    This topic was handled in issue `222 <https://github.com/Deltares/ra2ce/issues/222>`_
+
+Characteristics NetworkX
+""""""""""""""""""""""""
+- works well together with `geopandas`,
+- has different classes for graphs, multigraphs and directed (multi-)graphs,
+- offers many functions for graph manipulation and analysis.
+
+Characteristics igraph
+""""""""""""""""""""""
+- has a better performance than NetworkX,
+- less intuitive to use with Python and geopandas (e.g. working with coordinate systems is less straightforward),
+- less suited for dynamic graphs (indexing needs to be redone on extension and reduction of the graph).
+
+Conclusion
+""""""""""
+NetworkX is used on many places in the code.
+This, together with the differences in implementation, will require a thorough refactoring of the application for the benefit of a significant performance improvement.
+Therefore, for now, it was chosen not to work on replacing NetworkX with igraph.