.. draft
.. todo: review by christian

==========================================
Creating Sampling Design in QGIS
==========================================
In ecological studies, planning for sampling design is a crucial task to do 
to ensure that research objectives will be achieved. Many sampling designs 
have been developed and implemented in ecological studies (Sutherland 2006). 
Among of the widely used designs are random and stratified samplings or the 
combination of the two, which is called stratified random. These techniques 
are used to avoid bias of sampling in varying density of species 
populations in the study area.

To guide you in research planning, this section will demonstrate how to 
generate random points that can be used to identify possible areas for 
study.

.. Blurb on sampling design
.. http://en.wikipedia.org/wiki/Stratified_sampling

Random sampling of points
-------------------------------

1. Open QGIS and load the ``iba.shp`` polygon layer.  This layer is the study 
area you will conduct the sampling, we will create a new point layer of 
100 random points within the boundary of the polygon.

2. In the Menu select 
:menuselection:`Vector --> Research Tools -->` 
|random_points| :guilabel:`Random Points`.

.. image:: images/random_points_1.png
   :align: center
   :width: 200 pt

3. Select ``iba`` as your 
:guilabel:`Input Boundary Layer`.

4. Under the :guilabel:`Unstratified Sampling Design`, type ``100`` in the 
:guilabel:`Use this number of points`.

5. In the :guilabel:`Output Shapefile` click :guilabel:`Browse` and create a 
new Shapefile as ``random_100pts.shp``.  Click :guilabel:`OK`.

.. image:: images/random_points_2.png
   :align: center
   :width: 200 pt

6. Click :guilabel:`Yes` to add the new layer to your :guilabel:`Map Canvas`. 
Click :guilabel:`Close` to close the :guilabel:`Random Points` window.

.. image:: images/100_random_pts.png
   :align: center
   :width: 300 pt

The created point layer has 100 randomly placed points within the boundary of 
the polygon.

Stratified random sampling
-------------------------------

The same tool can also create a stratified sample of points based on the input 
boundary layer. 

1. In the Menu select
:menuselection:`Vector --> Research Tools -->` 
|random_points| :guilabel:`Random Points`.

2. In the :guilabel:`Output Shapefile` click :guilabel:`Browse` and create a 
new Shapefile as ``strat_50pts.shp``.  Click :guilabel:`OK`.

3. Under the :guilabel:`Stratified Sampling Design`, type ``50`` in the
:guilabel:`Use this number of points`. Click :guilabel:`OK`.

.. image:: images/random_points_3.png
   :align: center
   :width: 200 pt

This option will create 50 points for each polygon in the input boundary layer

The :guilabel:`Use this density of points` option is for a fixed density. 
The third :guilabel:`Use value from input field` option will use the value in 
a column in your attribute table to determine the number of sample points.


4. Click :guilabel:`Yes` to add the new layer to your :guilabel:`Map Canvas`. 
Click :guilabel:`Close` to close the :guilabel:`Random Points` window.

.. image:: images/50_stratrandom_pts.png
   :align: center
   :width: 300 pt

Explore the other tools available in the :menuselection:`Research Tools`.

+---------------------+-----------------+--------------------------------------+
| **Icon**            | **Tool**        | **Purpose**                          |
+=====================+=================+======================================+
| |random_selection|  | Random selection| Randomly select n number of          |
|                     |                 | features, or n percentage of features|
+---------------------+-----------------+--------------------------------------+
| |sub_selection|     | Random selection| Randomly select features within      |
|                     | within subsets  | subsets based on a unique ID field.  |
+---------------------+-----------------+--------------------------------------+
| |regular_points|    | Regular points  | Generate a regular grid of points    |
|                     |                 | over a specified region and export   |
|                     |                 | them as a point Shapefile.           |
+---------------------+-----------------+--------------------------------------+
| |vector_grid|       | Vector grid     | Generate a line or polygon grid      |
|                     |                 | based on user specified grid spacing.|
+---------------------+-----------------+--------------------------------------+
| |select_location|   | Select by       | Select features based on their       |
|                     | location        | location relative to another layer   |
|                     |                 | to form a new selection, or add or   |
|                     |                 | subtract from the current selection. |
+---------------------+-----------------+--------------------------------------+
| |layer_extent|      | Polygon from    | Create a single rectangular          |
|                     | layer extent    | polygon layer from the extent of an  |
|                     |                 | input raster or vector layer.        |
+---------------------+-----------------+--------------------------------------+


You can also save the sampling points as a ``GPX`` file which you can upload in 
your GPS device.

.. raw:: latex
   
   \pagebreak[4]