# Sketch Map Tool Exercise 5 - Heat Map Visualization ## Characteristics of the exercise :::{card} __Aim of this exercise:__ ^^^ Learn how to analyze your Sketch Map Tool Outputs by creating a heatmap. ::: ::::{grid} 2 :::{grid-item-card} #### Type of trainings exercise: This exercise can be used in online and presence training and is focused on an hands-on experience with QGIS spatial analysis tools. ::: :::{grid-item-card} #### Focus group (GIS-Knowledge Level) Medium-Advanced level (participants have worked with QGIS before) #### Phase of participatory /community mapping Analysing participatory mapping results ::: :::: ::::{grid} 2 :::{grid-item-card} #### Estimated time demand for the exercise. 1 hour ::: :::{grid-item-card} ### Available data - [Introductory slides on the Sketch Map Tool](https://nexus.heigit.org/repository/gis-training-resource-center/mobile_data_collection/sketch_map_tool/PPP/Introduction_Sketch_Map_Tool_21_03.pptx) - Download the data for this exercise [here](https://nexus.heigit.org/repository/gis-training-resource-center/mobile_data_collection/sketch_map_tool_training/Sketch_Map_Tool_Exercise_5.zip) and unzip the folder - In the data subfolder (`\data\input`), you will find the data you need to start the exercise (created raw map & 5 pre-marked and photographed maps). You will also find de geodata of the results (`\data\output`) and the intermediate result(`\data\temp`). - [Printable exercise factsheet](https://nexus.heigit.org/repository/gis-training-resource-center/mobile_data_collection/sketch_map_tool_training/Factsheet_printing_%20Ex_5.pdf) ::: :::: ## Instructions for the trainers :::{dropdown} __Trainers Corner__ ### Prepare the training - Online access and devices (PC) - QGIS installed on the computer - Take a look and make yourself familiar with the provided material for the exercise and the Sketch Map Tool in general. - Check out [How to do trainings?](../Trainers_corner/en_how_to_training.md) for some general tips on training conduction ```{Note} if you want to create additional or individual marked map examples you can use the empty Sketch Map provided in the materials. Also feel free to choose a completely different scenario by creating your own Sketch Map. ``` ### Conduct the training: __Introduction:__ - Introduce the idea, the aim and the general workflow of the Sketch Map Tool beforehand. - Provide access to the needed material. - check-in if there are questions or problems. - motivate fast participants to create a printable map in the end if they finish earlier than other participants __Wrap up:__ - Take some time at the end to wrap up and that several people present their result - Discuss the benefits of using heatmaps to analyze community mapping results - Refer to other chapters of the training platform and how users can benefit from it (e.g. visualisation or data analysis) - Leave time for open questions. :::: ### Exercise: Heat Map Visualization: Past Flood Delineation ### Scenario and Background Flood maps hold immense importance, especially in less privileged regions with limited regular surveying by official bodies/institutions. In these areas, where access to sophisticated technology and resources is often limited, flood maps provide a vital resource for understanding and managing flood risks. They empower communities to identify vulnerable areas, plan emergency response strategies, and implement mitigation measures. Flood maps facilitate informed decision-making, enabling communities to allocate resources effectively, prioritizing infrastructure development, and implementing early warning systems. By filling the gap in official surveying, flood maps play a crucial role in enhancing resilience, minimizing damages, and safeguarding lives and livelihoods in these vulnerable regions. The sketch map tool is a valuable tool for delineating flood areas within a community. It enables users to create hand-drawn or digitally generated maps to identify and outline areas prone to flooding. By incorporating local knowledge and observations, the tool empowers community members to actively participate in flood risk assessment and mitigation efforts. The Sketch Map Tool serves as a user-friendly and accessible solution for mapping flood areas, facilitating community engagement, and informing decision-making processes to enhance resilience and response strategies against flooding events. #### 1. Data Collection Imagine you were on a field trip in order to talk to people in the affected areas and let them draw maps about flood prone areas in their community. You are now back to your office and have 5 different flood maps that you have already scanned in. Please download the prepared maps [here](https://nexus.heigit.org/repository/gis-training-resource-center/mobile_data_collection/sketch_map_tool_training/Sketch_Map_Tool_Exercise_5.zip). Optional: You find the empty map [here](https://nexus.heigit.org/repository/gis-training-resource-center/mobile_data_collection/sketch_map_tool_training/Sketch_Map_Tool_Exercise_5.zip)(data/input). Feel free to draw some additional flood maps by printing the template out and drawing on it or by using a simple graphics editor. If you experience any problems during your use of the [Sketch Map Tool](https://sketch-map-tool.heigit.org/), please take a look at the [help page](https://sketch-map-tool.heigit.org/help). #### 2. Georeferencing and auto-extraction with the Sketch Map tool __Upload the sketch maps__ back to the tool’s website: Head to [sketch-map-tool.heigit.org](https://sketch-map-tool.heigit.org/) and choose `Digitize your Sketch maps` on the right. Upload all your sketches in .png or .jpg format. You can mark your sketches and simply drag and drop them into the window. The sketch maps are now being processed and georeferenced with the annotations extracted and vectorized. Download the vectors. You may use the ones we have prepared [here](). #### 3. Start your QGIS Project Open QGIS and __load your vector files__ by dragging and dropping them into the layer panel. __Explore__ the file by opening the attribute table. ```{Note} When you upload several marked Sketch Maps simultaneously, you will get one vector output containing all the markings of all Sketch Maps, while uploading your Sketch Maps one by one will provide you with one vector file for the marking in each Sketch Map. This information can be important for the planning phase of your mapping process. ``` Your vectorized sketches in the geojson format contain a feature for every extracted .png/.jpeg and markup color. In general, each marking in your sketch map will appear in the attribute table as one row, containing the name of your sketch map as well as the detected colour of the respective marking. Now, we want to visualise the degree of overlapping flood areas in order to create a heatmap. Generating a heatmap from my SKetch Map results helps us to identify patterns in the spatial data, in this case it will show us the overlapping of participants markings and help us identifying most at risk areas. For this purpose, we have to convert every feature to a distinct raster and then sum up the overlapping pixels in a new raster. In QGIS, you can do this in the following steps: #### 4. Rasterize 1. Add a column to your vector: - Open the __attribute table__ of your vector file and open the [`Field Calculator`](../Wiki/en_qgis_table_functions_wiki.md#calculate-field) by clicking on ![](../../../fig/mActionCalculateField.png). - In the field calculator dialog, check the `Create a new field` option, specify "fixed_val" as `Output field name` of the new field and choose "Whole number (integer)" as `Result field type`. - In the field calculator expression box, enter as value you want to assign to all features "1" (without quotes). - Click `Ok` ```{figure} ../../../fig/en_SMT_ex5_fixed_val.PNG --- height: 500px name: T align: center --- Field Calculator ``` ```{figure} ../../../fig/en_SMT_ex5_attribute_table.PNG --- height: 500px name: T align: center --- Attribute table with additional column"fixed_val" ``` 2. Convert your vectors to Rasters In the next step we want to __rasterise__ our vector layer. That means that we are essentially converting our vector geometries into a raster grid, where each cell represents a portion of the original vector features. Basically, we want to represent our flood polygons as a raster grid where each cell is assigned the value of 1, when it lies within a polygon, or 0, when it is outside of a polygon. In our resulting raster layer, the value 1 would then stand for "flood area". Click [here](../Wiki/en_qgis_geodata_types_wiki.md#types-of-geodata) for more information on the different geodata concepts. - In the top bar navigate via `Raster`, `Conversion` to `Rasterize (Vector to Raster)`. Alternatively, you can also search for `Rasterize (Vector to Raster)` in your __Processing Toolbox__. - As input layer, choose one of your vector layers. - __Important__: Set the green loop symbol left from the tool wrench activated. This ensures the iteration over each features (row) in your layer, meaning that __every feature in your layer is converted separately__. - Set `Field to use for a burn-in value` to your recently created field "fixed_val" and set `A fixed value to burn` to 1. The term "value to burn" refers to the pixel value that will be assigned to the rasterized representation of the features from the vector layer. This value is used to encode the presence of the features in the resulting raster image. - Set `Output raster size units` to "Pixels" and the `Width` and `Height` to 1000, respectively. (note: it might change automatically to a different pixel amount because of the output extent) - Set the Output Extent to the same as your input layer. Depending your QGIS version you might have to click on ![](../../../fig/Three_points.png), click on `Calculate from Layer` and choose your input layer. - Make sure to set the `Assign a specified nodata value` to "not set". You need to delete the 0 and eventually "no set" will appear. - Finally, determine the path where you save the file and name of your rasterized output files under `Rasterized` by clicking on ![](../../../fig/Three_points.png) -> `Save to File` - Click `Run` ```{figure} ../../../fig/en_SMT_ex5_rasterize.PNG --- height: 500px name: T align: center --- Rasterize ``` You should end up with a binary raster for every sketch map you georeferenced. All flooded areas should be represented by pixels of value 1, while non-flooded areas are represented by 0. ```{figure} ../../../fig/en_SMT_ex5_rasterize_result.PNG --- height: 500px name: T align: center --- Output Rasterize ``` #### 5. Raster Calculator We will now sum up all our output rasters: In the top bar, navigate via `Raster`to `Raster Calculator`. In the `Raster Calculator Expression`, sum up the 10 rasters you rasterized from your vectors. You can double-click on each raster in the `Raster Bands` window and add the operator "+": >More detailed explanation or video maybe? ```{figure} ../../../fig/en_SMT_ex5_raster_caclulator.PNG --- height: 500px name: T align: center --- Raster Calculator ``` Finally, click on ![](../../../fig/Three_points.png) next to `Output layer` and navigate to your results folder to save your output. Then, click `OK`. ```{figure} ../../../fig/en_SMT_ex5_sum_result.PNG --- height: 500px name: T align: center --- Output sum of rasters ``` Based on the __sum of the rasters__, we have now created just one raster that will have a __pixel value of 0__ if no flooding been reported; a __pixel value of 1__ if one person/sketch map reported a flood, a __pixel value of 2__ if two persons/sketch maps reported a flood at that location, and so on. #### 6. Visualization In order to visualize the result, right-click on your layer and navigate to `Properties` -> `Symbology`. In the `Band Rendering` section, you can for example choose as `Render Type` "Singleband pseudocolor", and, next to `Color ramp`, choose a color ramp of your choice. In the `Layer Rendering` section, you can adapt your `Blending mode`. Play around with the options and the `Brightness` and `Contrast` section in order to find a good match in order to visualize your findings comprehensibly. Please revise [XX Chapter]() in order to lean more about options you have to visualize your raster data. ```{figure} ../../../fig/en_SMT_ex5_raster_symbology.PNG --- height: 500px name: T align: center --- Raster Symbology ``` You will realize that you 0 Values (=no flooding) are still colored, but they are not of interest for us, since we are interested in visualizing the flood extent polygons. In order to make them transparent, you can navigate in `Properties` -> `Transparency` where you'll see an option for `Transparent pixel list`. Click on `+` to specify the pixels values you want to be transparent. In our case, we want all pixels with the value '0' to be 100% transparent. Once you've set the transparency settings as desired, click `Apply` to see the changes in the map canvas. If you're satisfied, click `OK` to close the Layer Properties dialog. ```{figure} ../../../fig/en_SMT_ex5_raster_transparency.PNG --- height: 500px name: T align: center --- Raster Transparency ``` Your resulting heatmap could look something like this. The darker the color, the more people/sketch maps indicated flooded areas at that location: ```{figure} ../../../fig/en_SMT_ex5_heatmap.PNG --- height: 500px name: T align: center --- Raster Transparency ``` ```{note} Keep in mind that what you are seeing on your screen is not a map that is ready to be printed or distributed. You could now create a printable map. Take a look at the chapter on the [print layout](../Module_4/en_qgis_map_design_2.md) and the [wiki](../Wiki/en_qgis_map_making_wiki.md) to do so. ```