QGIS is a free and open-source Geographic Information System (GIS) that allows us to perform advanced geographical analysis of the data obtained from one or multiple Meteobike systems. It runs on Linux, Mac OSX, Windows and other systems.
Download QGIS and follow installation instructions, incluing the correct Python version.
In a first step we would like to import and map your Meteobike dataset.
Open QGIS and create a new project using Project > New >. Save the new project under Project > Save As....
In the 'Browser' to the left, click on XYZ Tiles and double click OpenStreetMap. Open Street Map tiles will be shown. At first, you will see the entire Earth. Use the cursor and zoom fuction to navigate to the city of your data.
You can import any .csv file into QGIS. This means, you can directly input the raw datafiles from the Meteobike system. Alternatively, you can also data that has been filtered and merged into a single file from multiple systems. Use Menu Layer > Add Layer > Add Delimited Text Layer... to add data from one or multiple meteobike systems.
Select the file of your interest (by clicking on the ...-button in the upper right).
Under 'File Format' select CSV (comma separated values), under 'Record and Field Options' select First record has field names and Detect field types. Under 'Geometry Definition' it should automatically select 'Longitude' as x field and 'Latitude' as y field. 'Sample Data' displays your measurement dataset. Check if everything looks OK and then click Add.
Your measurements will be displayed as single points. Right click on the new layer and select Properties... to customize the display.
You can display the measured values as numeric labels next to the points. To do this, select 'Labels' and choose for example the 'Temperature' field to show numeric values of temperatures measured at that point:
Each point is displayed along with the measured temperature:
You can further color-code the points based on measured temperatures. Right click again on the new layer and select Properties.... Here you can select Symbology and choose Graduated as the model:
Under 'Column' select the field from the Meteobike dataset you would like to colorize (e.g. temperature differences). Unter 'Method' choose Color. Under 'Color ramp' you can choose from a variety of color bars (and also invert them, as done in the example). Below is the list that assigns colors to values. The example uses Quantile mapping with 13 classes. Click Classify to update the color ramp, then OK to apply it to the map:
Next assume, you would like to calculate average temperatures measured in different parks and contrast them. To d this, you need to select points based on geographic location - in some areas in complex, irregular shapes. One option to achieve this is through a 'spatial join' - a basic geographic operation selecting elements that are within another one.
First you have to define the geographic areas in which you would like to sample measurements. In our example we will select temperatures in different parks, however, this approach can be applied to any other geographic dataset - including imported shape files, 'Local Climate Zones' (LCZ) or raster elements (see below for raster examples).
Before you draw the areas, you must create a new layer. Select Menu Layer > Create Layer > New Shapefile Layer.... Under 'File name' select an appropriate name (here, we will call it parks.shp) and use the ...-button to store the shape file locally. As 'Geometry type' choose Polygon.
You can later add properties to each polygon such as a name of the park (or LCZ, size of the park etc.). As an example, we will now simply create a field Name to enter the known local name of each park. Enter "Name" and and click Add to Fields List. Then click OK to create the shape file.
Under Layers you will now see a new layer called "Parks". Right-click on the 'Parks'-layer and select Toggle Editing. Then click the polygon-drawing icon (
) to draw a first park area:
Close the polygon by right-clicking. A dialog will appear to enter ID and Name (and any other properties you have previously defined). Enter and click OK:
You can finish here, or add additional polygons for additional parks. In the end, after drawing one or multiple polygons, click again on Toggle Edit and save the shape file layer.
In a next step you would like to select all measurements inside the selected polygon and calculate statistics based on only those points taht fall within the area. This is a more complex task, so you need the "Toolbox" for this. Select menu Processing > Toolbox. The toolbox appears on the right hand side of the map:
In the toolbox choose select Vector general > Join attributes by location (summary):
As 'Input Layer' choose your polygon-layer (i.e. 'parks.shp'). As join layer choose your points with temperatures from the meteobike dataset. Under 'Geometric predictate' you should choose contains and under 'Fields to summarize' you select the field from the meteobike dataset to create statistics from (i.e. Temperature). Then click on run. This will first select all points that fall within the polygon and then calculate statistics from those points and write them to the polygon as attributes. A new layer Joined layer will be created. You can rename the layer.
Right-click on the new Joined layer and select Open Attribute Table. You will now see a list of all parks with the statistics of the points (i.e. temperatures) displayed:
Essentially the same procedure can also be used to aggregate the measured datapoints in a gridded map. QGIS has an option to create different grids as polygon layers. To create a grid, select menu Vector > Research Tools > Create grid...:
Because it is trendy, you can choose as grid type Hexagon (polygon). To define the area that should be gridded, you can Select canvas extent by clicking on the ... button. Choose an appropriate grid size, e.g. 250 m and click Run. A new grid layer will be generated.
In the next step you can repeat what has been described above for the parks, but replace the parks with the grid polygons - Go to the Toolbox and select again Vector general > Join attributes by location (summary). As 'Input Layer' choose the newly created grid layer )(the hexagons). As join layer choose again your points with temperatures from the meteobike dataset. It is recommended to select a limited number fields for startstics (only the ones you need) otherwise the operation will take a long time to be computed.
A new grid layer will be generated which is showing only cells where measurements are located within. You can right-click the new layer and choose Properties... attribute a color coding to the grid cells under Symbology. Choose Graduated as the model.
This way you finally get fancy heat map:
Some data sources such as Digital Elevation Models (DEM) or vegetation indices are provided in raster format, rather than vector format. In some application we would like to attribute values from rasters to our Meteobike measurements, or perform more detailed releif analysis.
As an example, we can import a DEM and combine it with the measurements from our Meteobikes. A free source for elevation data ASTER Global DEM V2 is the Global Data Explorer, which can be obtained from a server at USGS and NASA. Use the navigation tools on the website to zoom to the area of your interest. With the rectangular selection tool you can select an area to be downloaded:
If you create a free user account, you can download the ASTER Global DEM V2 in GeoTIFF format:
Save the '.tif' file locally on your machine. Then import the ASTER DEM into QGIS using the menu Layer > Add Layer > Àdd Raster Layer. Choose the previous '.tif' file with the ASTER Global DEM V2 as source:
Right-click to change the appearance of the DEM to have different elevations displayed differently. To add countour lines go to the menu Raster > Extraction > Contour....
You can now display your Meteobike data along the digital elevation model:
To attribute data from a raster dataset to the point-measurements, go to the menu Processing > Toolbox. As an example, we will now attribute the elevation from the DEM to each measurement location of the Meteobike. In the Toolbox choose SAGA > Vector <-> raster > Add raster values to points. SAGA (System for Automated Geoscientific Analyses) is a free, hybrid, cross-platform GIS software that is included in QGIS as a plug-in. It contains many more specific scientific tools to analyze data.
Choose the Meteobike Dataset as the 'Points' and the DEM as the 'Grid'. As points do not fall directly in teh center of pixels, you may ant to interpolate the data between pixels (e.g. here 'Interpolation' [1] Bilinear interpolation). Click Run to create a new point layer that has the original Meteobike data combined with the data from the DEM (elevation). You find the elevation from the DEM in the very last column of the 'Attribute Table'. You can now display the data with the elevation from the DEM.
Note that the meteobikes already measured elevation (GPS Altitude) that should actually match the elevation data from the DEM - so there is currently no added value of doing this. Nevetheless, you can apply this procedure to any raster dataset (slope, catchment area, land cover data). There is a whole range of useful terrain analysis tools available in QGIS / SAGA for further analysis.