.. _8.2:

Number of People affected by flooding 
=====================================

The model we are going to use is reported in :numref:`8.2.1` .

.. _8.2.1:

.. figure:: /img/8/8.2.1.png
   :align: center

   -- Model Designer - final model

The first step when building a model is to set the input layers (:numref:`8.2.2`) . In this case we will use the Population Raster Dataset (“Pop_UTM_Clipped”) **(1)** and the layer with the flooded area (“ObservedEvent_UTM”) **(2)**. Both inputs have been set as **Mandatory**.

.. _8.2.2:

.. figure:: /img/8/8.2.2.png
   :align: center

   -- Model Designer - input layers

The next step (:numref:`8.2.3`) involves the geometry fix algorithm. You can notice that the Input of this block is connected to the flooded area layer, this will tell that the geometry fix is applied over that layer. The geometry fix  algorithm **(1)** is used to repair issues or errors that can emerge when working with vector data, especially when conversion or digitalizations procedures are applied.

.. _8.2.3:

.. figure:: /img/8/8.2.3.png
   :align: center

   -- Model Designer - geometry fix

The next step is depicted in (:numref:`8.2.4`).  At first we will use the **Clip raster by mask layer** tool **(1)** in order to reduce the computational burden of the following operations. As you can see the input of this block is composed of the population layer, which is the layer we are going to clip, and the flooded area layer with fixed geometries. As a second step we will convert the obtained raster layer to a vector format **(2)**, with this procedure each cell of the raster will become a polygon. In this procedure we add a column to maintain the information (the number of people in that cell) regarding that cell.

.. _8.2.4:

.. figure:: /img/8/8.2.4.png
   :align: center


   -- Model Designer - clip and polygonize

In (:numref:`8.2.5`) , the next step is shown. This step involves cutting the Population layer converted to vector over the flooded area **(1)**.

.. _8.2.5:

.. figure:: /img/8/8.2.5.png
   :align: center


   -- Model Designer - clip

The last step is depicted in (:numref:`8.2.6`) and involves the **Aggregate** algorithm **(1)**. This algorithm combines features based on a spatial relationship or another attribute, in this particular case we use the aggregate algorithm to aggregate all features since the input of this block is composed of a vector layer with only the number of population features. Finally, the output of the model is the “Affected_Population” layer.

.. _8.2.6:

.. figure:: /img/8/8.2.6.png
   :align: center

   -- Model Designer - aggregate and population computation

Click on the green player button to run the algorithm **(1)** (:numref:`8.2.7`) . You will be asked to choose the layer that will represent the input to the model. Set the flooded_area field as “ObservedEvent_UTM” **(2)** and the Population Raster Dataset field as “Pop_UTM_Clipped” **(3)**. Once done, click on Run **(4)**.

.. _8.2.7:

.. figure:: /img/8/8.2.7.png
   :align: center

   -- Model Designer - Run Model

The obtained results show that 823 people were involved in the flood event.