Creating a Colorized River Basin Map (QGIS3)

In this tutorial, we will learn the QGIS workflow to create artistic river maps for your own country or region using openly available hydrological data.

Nota

This tutorial is inspired by the beautiful maps produced by Grasshopper Geography. I own one of their prints and you too can support their work by purchasing one of their maps from their online store.

Overview of the task

In this tutorial, we will take data layers of basins and rivers from HydroSHEDS and create a basin map for rivers of India.

Other skills you will learn

• How to assign projection to a vector layer with incorrect or missing projection.

• How to add multiple layers in a single GeoPackage.

• How to add a “Made with QGIS” badge to your map.

Get the data

HydroSHEDS provides global hydrological datasets suitable for regional and global applications. The data layers are derived from hydrologically conditioned DEM from SRTM.

Basin Boundaries

HydroBasins provides polygon boundaries of basins for different continents. The boundaries are hierarchical – each basin at Level N is further subdivided into smaller basins at Level N+1. For this tutorial, we will use the Level 6 basin boundaries. You can use different level depending on your region and type of map you want to create. Visit the HydroBASINS page and download the zip file for your region.

Nota

HydroSHEDS basin boundaries are derived from SRTM data which is over 20 years old at this point. The basin boundaries may not match the official basin boundaries in your region. You can substitute HydroBasins data with polygons from official sources when available.

River Network

HydroRIVERS provides a line shapefile representing the river network. Visit the HydroRIVERS page and download the zip file for your region of interest.

Administrative Boundary

We will clip the HydroSHEDS data to the boundary of your chosen region. In this tutorial, we want to create a river basin map of India, so we will get the boundary shapefile from Survey of India. Visit the Outline Maps of India page and download the India International Boundary Vector Format. If you need admin boundaries for other countries or states, you can get them from GADM or geoBoundaries.

Once all the files are downloaded, unzip them and copy them to a folder. You should now have 3 shapefiles: hybas_as_lev06_v1c.shp, HydroRIVERS_v10_as.shp and admin boundaries `polymap15m_area.shp`.

Data Sources: [HYDROSHEDS], [SOI]

Procedure

1. Open QGIS and locate the downloaded files in the QGIS Browser. Drag and drop hybas_as_lev06_v1c.shp and HydroRIVERS_v10_as.shp to the canvas.

2. Locate the administrative boundaries shapefile polymap15m_area.shp and drag-and-drop it to the canvas.

3. The HydroSHEDS data layers have some features with invalid geometries Let’s fix them proceeding further. Open the Processing Toolbox from Processing ‣ Toolbox. Search and locate the Vector geometry ‣ Fix geometries tool. Double-click to launch it.

Nota

You can review the tutorial Handling Invalid Geometries (QGIS3) to learn more about the causes and fixes for invalid geometries.

4. Select hybas_as_lev06_v1c as the Input layer. Click the … button next to Fixed geometries and select Save to GeoPackage….

5. Browse to the location where you want to save the output data and enter the name data.gpkg. Click Save. You will be prompted to enter a Layer name. Enter basins_fixed. Click OK. Next click Run to run the algorithm and generate the output layer.

6. Repeat the step for the HydroRIVERS_v10_as layer. Select the same GeoPackage data.gpkg that was created in the previous step. Do not worry if you get a message indicating that the file will be overwritten. QGIS will not overwrite the file, but append a new layer to the same GeoPackage. This time use rivers_fixed as the Layer name.

7. The polymap15m_area layer comes with a projection that is not recognized by QGIS. We will assign a known projection to this layer. Search and locate the Vector general ‣ Assign projection tool and double-click to open it.

Nota

Remember that Assign projection tool does not reproject the layer but simply adds the correct projection information to an existing georeferenced layer with missing or incorrect projection. Use the Reproject layer tool if you want to change the CRS of a layer.

8. Select polymap15m_area as the Input layer. Click the Select CRS button and search for the EPSG:7755 - WGS 84 / India NSF LCC projection and select it. Click the … button next to Assigned CRS and select Save to GeoPackage….

9. Select the same GeoPackage data.gpkg and enter the layer name admin_boundary_fixed. Click Run.

10. You will now have 3 new layers basins_fixed, rivers_fixed and admin_boundary_fixed loaded to the Layers panel in QGIS. Hold the Shift key and select all remaining layers. Right-click and choose Remove Layer….

11. We will now clip the basins and rivers layers to the administrative boundary. Search and locate the Vector overlay ‣ Clip tool from the Processing Toolbox. Double-click to open it.

12. Select basins_fixed as the Input layer and admin_boundary_fixed as the Overlay layer. Save the output to the same GeoPackage data.gpkg as the layer basins_clipped. Click Run.

13. Once the processing finishes, repeat the process with the rivers_fixed layer as the Input layer. Save the output to the same geopackage data.gpkg as the layer rivers_clipped. Click Run.

14. You will now have 2 new layers basins_clipped and rivers_clipped, as well as admin_boundary_fixed layer loaded to the Layers panel in QGIS. Hold the Shift key and select all remaining layers. Right-click and choose Remove Layer….

15. Before we proceed further, let’s save the project. QGIS allows you to save a project inside of a GeoPackage - making it very convenient to avoid managing additional files. Go to Project ‣ Save To ‣ GeoPackage….

16. In the Save project to GeoPackage dialog, click the … button next to Connection and browse to the existing data.gpkg file. Enter the name rivers_basin_map as the Project name. Click OK.

17. Once saved, you can expand the data.gpkg in the Browser panel and see that the QGIS project is now saved inside the GeoPackage. Users of this GeoPackage can now open the project directly from the GeoPackage.

18. To create our colorized map, we need to color all the basins such that no adjacent basins have the same color. QGIS has a tool to do just that. Open the Cartography ‣ Topological coloring tool from the Processing Toolbox.

19. Select basins_clipped as the Input layer. Leave other options to their default values. Save the output to the same GeoPackage data.gpkg as the layer basins_with_color. Click Run.

20. Once the processing finishes, a new layer basins_with_color will be loaded to the Layers panel. Right-click the layer and select Open Attribute Table. You will notice that the layer has a new attribute named color_id with an integer value. Assigning a unique color to each integer value will result in topolocal coloring of the layer.

21. We want to transfer the color id for the basin to all the rivers contained within it. Open the Vector general ‣ Join attributes by location tool from the Processing Toolbox.

22. Here we want to select rivers_clipped as the layer to Join to features in and basins_with_color as the layer for By comparing to. In the Fields to add section, click the … button and select the color_id field. Save the output to the data.gpkg geopackage as the layer rivers_with_color. Click Run.

23. Once the processing finishes, a new layer rivers_with_color will be loaded to the Layers panel. Now it is time to apply the symbology. Select the admin_boundary_fixed layer and click the Open Layer Styling Panel button in the Layers panel. Change the color to black.

24. Next, select the rivers_with_color layer and select the Categorized renderer.

25. Select color_id as the Value and click Classify. You will see the rivers in different basins will be assigned a different color.

Nota

If you are not happy with the randomly chosen colors, you can click the Symbol for individual values in the list below and choose your own color.

26. The default lines are too thick for our map. Let’s change it. Hold the Shift key and select all the symbols in the list. Click the Symbol to open the Symbol Settings.

27. Click on Simple Line and change the stroke width to 0.1. The map will look much better now.

28. We can improve the map by assigning different widths to the rivers based on their size. The rivers_with_color layer has a field ORD_STRA containing the value of the Strahler Order of the river. The larger the number, the bigger the river. We will use the Assistant to help us use the value of the strahler order to an appropriate stroke width. Click the Data defined override button next to Stroke width and select Assistant….

29. In the Input section, select the ORD_STRA field as the Source with Values from 1 to to 6. In the Output section, choose Size from as 0.05 and to as 0.2. The map will update dynamically as you enter the values. You may have to adjust these values depending on your region. Once you are happy with the map, click the Back button.

30. You will notice that the Data defined override button for Stroke width is now yellow, indicating an active override has been applied to this setting.

31. Our colorized river basin map is now ready. Let’s put this map in a layout so we can export a high-resolution version with other map elements. Go to Project ‣ New Print Layout…. When prompted to enter a name, leave it blank and click OK.

32. In the Layout 1 window, right-click on the blank canvas and choose Page Properties….

33. Choose A4 as the Size. Change the Background color to black.

34. Go to Add Item ‣ Add Map.

35. Hold the left mouse button and select a region on the canvas where you want the map to be placed.

36. Once the map appears, scroll down in the Item Properties tab and turn off the Background.

Nota

If you do not see the Item Properties tab or close it by accident, you can get it back by going to View ‣ Panels ‣ Item Properties in the Layout menu.

37. Let’s adjust the map extents. Click on the Interactively Edit Map Extent button and then use the mouse to pan the map. You can also use your scroll wheel to adjust the zoom. If you want more finer control on the Zoom, adjust the Scale value manually. Repeat till you are happy with the map placement.

38. Next we will add a QGIS logo to the map. Go to Add Item ‣ Add Picture.

39. Draw a rectangle where you want to place the logo. In the Item Properties dialog, locate the logos icon group. Select the Made with QGIS logo.

40. Next, we will add a label with data credits. Go to Add Item ‣ Add Label. Enter the text for data credits and adjust the font and label alignment.

41. Once you are ready to export the results, go to Layout ‣ Export as Image…. Browse to a folder on your computer where you want to save the PNG image and enter the name river_basins.png.

42. Choose 300 dpi as the Export resolution and click Save.

43. Once the export finishes, you will have your final map image at the chosen location.

44. Here’s the final PNG image that we created using QGIS and open datasets.

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