add backend intro and how-to diagram

doc/internals/how-to-add-new-backend.rst

@@ -4,7 +4,7 @@ How to add a new backend
 ------------------------
 
 Adding a new backend for read support to Xarray does not require
-to integrate any code in Xarray; all you need to do is:
+one to integrate any code in Xarray; all you need to do is:
 
 - Create a class that inherits from Xarray :py:class:`~xarray.backends.BackendEntrypoint`
   and implements the method ``open_dataset`` see :ref:`RST backend_entrypoint`

doc/user-guide/computation.rst

@@ -426,7 +426,7 @@ However, the functions also take missing values in the data into account:
 
 .. ipython:: python
 
-    data = xr.DataArray([np.NaN, 2, 4])
+    data = xr.DataArray([np.nan, 2, 4])
     weights = xr.DataArray([8, 1, 1])
 
     data.weighted(weights).mean()

doc/user-guide/io.rst

@@ -19,6 +19,80 @@ format (recommended).
 
     np.random.seed(123456)
 
+You can `read different types of files <https://docs.xarray.dev/en/stable/user-guide/io.html>`_
+in `xr.open_dataset` by specifying the engine to be used:
+
+```python
+import xarray as xr
+xr.open_dataset("my_file.grib" , engine="cfgrib")
+```
+
+The "engine" provides a set of instructions that tells xarray how
+to read the data and pack them into a `dataset` (or `dataarray`).
+These instructions are stored in an underlying "backend".
+
+Xarray comes with several backends that cover many common data formats.
+Many more backends are available via external libraries, or you can `write your own <https://docs.xarray.dev/en/stable/internals/how-to-add-new-backend.html>`_.
+This diagram aims to help you determine - based on the format of the file you'd like to read -
+which type of backend you're using and how to use it.
+
+The rectangular boxes are clickable for more information.
+Following the diagram is detailed information on many popular backends.
+You can learn more about using and developing backends in the
+`Xarray tutorial JupyterBook <https://tutorial.xarray.dev/advanced/backends/backends.html>_`.
+
+.. mermaid::
+    :alt: Flowchart illustrating how to choose the right backend engine to read your data
+
+    flowchart LR
+        built-in-eng["`Is your data stored in one of these formats?
+            fa:fa-check-square netCDF4 (**netcdf4**)
+            fa:fa-check-square netCDF3 (**scipy**)
+            fa:fa-check-square Zarr (**zarr**)
+            fa:fa-check-square DODS/OPeNDAP (**pydap**)
+            fa:fa-check-square HDF5 (**h5netcdf**)
+            `"]
+
+        built-in("`You're in luck! Xarray bundles a backend for this format.
+            Open data using *xr.open_dataset()*. We recommend
+            always setting the engine you want to use.`")
+
+        installed-eng["`One of these formats?
+            fa:fa-check-square GRIB (**cfgrib**)
+            fa:fa-check-square TileDB (**tiledb**)
+            fa:fa-check-square GeoTIFF, JPEG-2000, ESRI-hdf (**rioxarray**, via GDAL)
+            fa:fa-check-square Sentinel-1 SAFE (**xarray-sentinel**)
+            fa:fa-check-square ...
+            `"]
+
+        installed("`Install the package indicated in parentheses
+            to your Python environment. Restart the kernel
+            and use *xr.open_dataset(files, engine='rioxarray')*`")
+
+        other("`Ask around to see if someone in your data community
+            has created an Xarray backend for your data type.
+            If not, you may need to create your own or consider
+            exporting your data to a more common format.`")
+
+        built-in-eng -->|Yes| built-in
+        built-in-eng -->|No| installed-eng
+
+        installed-eng -->|Yes| installed
+        installed-eng -->|No| other
+
+        click built-in-eng "https://docs.xarray.dev/en/stable/getting-started-guide/faq.html#how-do-i-open-format-x-file-as-an-xarray-dataset"
+        click installed-eng "https://corteva.github.io/rioxarray/stable/getting_started/getting_started.html#rioxarray"
+        click other "https://docs.xarray.dev/en/stable/internals/how-to-add-new-backend.html"
+
+        classDef quesNodefmt fill:#9DEEF4,stroke:#206C89,text-align:left
+        class built-in-eng,installed-eng quesNodefmt
+
+        classDef ansNodefmt fill:#FFAA05,stroke:#E37F17,text-align:left,white-space:nowrap
+        class built-in,installed,other ansNodefmt
+
+        linkStyle default font-size:20pt,color:#206C89
+
+
 .. _io.netcdf:
 
 netCDF

doc/whats-new.rst

@@ -42,7 +42,9 @@ Bug fixes
 Documentation
 ~~~~~~~~~~~~~
 
-- Adds a flow-chart diagram to help users navigate help resources (`Discussion #8990 <https://github.com/pydata/xarray/discussions/8990>`_).
+- Adds intro to backend section of docs, including a flow-chart to navigate types of backends (:pull:`9175`).
+  By `Jessica Scheick <https://github.com/jessicas11>`_.
+- Adds a flow-chart diagram to help users navigate help resources (`Discussion #8990 <https://github.com/pydata/xarray/discussions/8990>`_, :pull:`9147`).
   By `Jessica Scheick <https://github.com/jessicas11>`_.
 - Improvements to Zarr & chunking docs (:pull:`9139`, :pull:`9140`, :pull:`9132`)
   By `Maximilian Roos <https://github.com/max-sixty>`_