11. Shallow n Spatial
==================================

.. image:: ../../../img/gridtools/Spatial-Shallow/spatia003.png


A spatially variable shallow n-value enables the flow roughness to be depth integrated to enable
high n-values at shallow flow depths. Polygons can be applied to select individual or groups of grid elements to
supersede the global n-value as in the case for streets and parking lots.

.. note:: The value can be globally assigned in the FLO-2D Control and Tolerance Variables window.

Digitize or Copy Data
---------------------

1. Select the Shallow-n Areas
   layer and click edit.

2. Create or copy the polygons
   that represent the shallow roughness areas to the layer and save them.

.. image:: ../../../img/gridtools/Spatial-Shallow/spatia002.png

.. image:: ../../../img/gridtools/Spatial-Shallow/image4.png


Sample Data
-----------

1. Click the Sampling Spatial Shallow-n Values
   button and then OK once the process is complete.

.. image:: ../../../img/gridtools/Spatial-Shallow/spatia003.png


.. image:: ../../../img/gridtools/Spatial-Shallow/spatia004.png


Troubleshooting
---------------

1. Create the shallow-n polygons
   if they are missing from the Shallow-n Areas layer.

2. If the Grid layer is empty,
   create a grid and try again.

3. If a Python error appears during the sampling process, the attribute table may be missing.
   Save and reload the project into QGIS and try again.