|LS| Combining the Analyses =============================================================================== Using the vectorized results of the raster analysis will allow you to select only those buildings on suitable terrain. **The goal for this lesson:** To use the vectorized terrain results to select suitable plots. |moderate| |TY| ------------------------------------------------------------------------------- #. Save your current map (:file:`raster_analysis.qgs`). #. Open the map which you created during the vector analysis earlier (you should have saved the file as :file:`analysis.qgs`). #. In the :guilabel:`Layers` panel, enable these layers: * :guilabel:`hillshade`, * :guilabel:`solution` (or :guilabel:`buildings_over_100`) #. In addition to these layers, which should already be loaded in the map from when you worked on it before, also add the :file:`suitable_terrain.shp` dataset. #. If you are missing some layers, you should find them in :file:`exercise_data/residential_development/` #. Use the :guilabel:`Intersection` tool (:menuselection:`Vector --> Geoprocessing Tools`) to create a new vector layer called :file:`new_solution.shp` which contains only those buildings which intersect the :guilabel:`suitable_terrain` layer. You should now have a layer showing certain buildings as your solution, for example: .. figure:: img/new_solution_example.png :align: center |moderate| |TY| Inspecting the Results ------------------------------------------------------------------------------- Look at each of the buildings in your :guilabel:`new_solution` layer. Compare them with the :guilabel:`suitable_terrain` layer by changing the symbology for the :guilabel:`new_solution` layer so that it has outlines only. What do you notice about some of the buildings? Are they all suitable just because they intersect with the :guilabel:`suitable_terrain` layer? Why or why not? Which ones would you deem to be unsuitable? .. admonition:: Answer :class: dropdown You may notice that some of the buildings in your :file:`new_solution` layer have been "sliced" by the :guilabel:`Intersection` tool. This shows that only part of the building - and therefore only part of the property - lies on suitable terrain. We can therefore sensibly eliminate those buildings from our dataset. |moderate| |TY| Refining the Analysis ------------------------------------------------------------------------------- You can see from the results that some buildings which were included were not really suitable, so we can now refine the analysis. We want to ensure that our analysis returns only those buildings which fall entirely within the :guilabel:`suitable_terrain` layer. How would you achieve this? Use one or more Vector Analysis tools and remember that our buildings are all over 100m squared in size. .. admonition:: Answer :class: dropdown At the moment, your analysis should look something like this: .. figure:: img/new_solution_example.png :align: center Consider a circular area, continuous for 100 meters in all directions. .. figure:: img/circle_100.png :align: center If it is greater than 100 meters in radius, then subtracting 100 meters from its size (from all directions) will result in a part of it being left in the middle. .. figure:: img/circle_with_remainder.png :align: center Therefore, you can run an *interior buffer* of 100 meters on your existing :guilabel:`suitable_terrain` vector layer. In the output of the buffer function, whatever remains of the original layer will represent areas where there is suitable terrain for 100 meters beyond. To demonstrate: #. Go to :menuselection:`Vector --> Geoprocessing Tools --> Buffer(s)` to open the Buffer(s) dialog. #. Set it up like this: .. figure:: img/suitable_terrain_buffer.png :align: center #. Use the :guilabel:`suitable_terrain` layer with ``10`` segments and a buffer distance of ``-100``. (The distance is automatically in meters because your map is using a projected CRS.) #. Save the output in :file:`exercise_data/residential_development/` as :file:`suitable_terrain_continuous100m.shp`. #. If necessary, move the new layer above your original :guilabel:`suitable_terrain` layer. Your results will look like something like this: .. figure:: img/suitable_buffer_results.png :align: center #. Now use the :guilabel:`Select by Location` tool (:menuselection:`Vector --> Research Tools --> Select by location`). #. Set up like this: .. figure:: img/select_by_location.png :align: center #. Select features in :guilabel:`new_solution` that intersect features in :guilabel:`suitable_terrain_continuous100m.shp`. This is the result: .. figure:: img/buffer_select_result.png :align: center The yellow buildings are selected. Although some of the buildings fall partly outside the new :guilabel:`suitable_terrain_continuous100m` layer, they lie well within the original :guilabel:`suitable_terrain` layer and therefore meet all of our requirements. #. Save the selection under :file:`exercise_data/residential_development/` as :file:`final_answer.shp`. |IC| ------------------------------------------------------------------------------- You have now answered the original research question, and can offer an opinion (with reasons, backed by analysis) for a recommendation regarding which property to develop. |WN| ------------------------------------------------------------------------------- Next you will present these results as part of your second assignment. .. Substitutions definitions - AVOID EDITING PAST THIS LINE This will be automatically updated by the find_set_subst.py script. If you need to create a new substitution manually, please add it also to the substitutions.txt file in the source folder. .. |IC| replace:: In Conclusion .. |LS| replace:: Lesson: .. |TY| replace:: Try Yourself .. |WN| replace:: What's Next? .. |moderate| image:: /static/common/moderate.png