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QGIS: Mobile Mapping

UQ Library 2024-09-16

Setting up

This tutorial is designed for QGIS 3.22. If you need to install it on your computer, got to the QGIS website.

Open QGIS and create a new project with Project > New. Let’s straight away save our project: Project > Save. We should create a new folder, let’s call it “qgis_mobile”. This where our project and all the saved data will live. Folder structure is very important for keeping you data tidy, but also for ease of sharing your project with others. You simply need to zip the project folder if you need to share it. We can save our .qgz project file here, named “qgis_mobile_map” for example. I also recommend creating a Data folder, for all of your downloaded data. And creating a Products folder, for all the things we create today. Your .qgz file should always be in the highest level folder, so it’s only looking down into folders for data, not back out.

In QGIS 3.10 and above this will automatically set the project home too. To do this manually, you can go to Project > Properties > General and set Project home to the same folder. This is where we can also give the project a title.

Let’s also add an OpenStreetMap basemap to locate ourselves on the globe: Browser panel > XYZ Tiles > OpenStreetMap (double-click, or drag and drop into the Layers panel).

Install Avenza Maps on your phone

Avenza Maps is a mobile based offline mapping app you can use on your smartphone.

For Android Devices: https://play.google.com/store/apps/details?id=com.Avenza&hl=en_AU

For Apple Devices: https://apps.apple.com/au/app/avenza-maps/id388424049

There are alternatives to Avenza Maps out there, such as QField or Input (MerginMaps) which are specifically created for use with QGIS on your mobile. However, we will be using Avenza today for its simplicity.

Get some data

We’re going to explore a number of different online spatial data repositories.

DEM

A Digital Elevation Model (DEM) is a common example of raster data, i.e. grid data that contains a value in each cell (a bit like the pixels in a coloured picture).

For this tutorial, we are using a DEM sourced from ELVIS - Geoscience Australia’s ELeVation Information System.

  • Go to http://www.ga.gov.au/elvis/
  • Search for “St Lucia” in the Location Search search box and select the first result
  • Click Order Data
  • Choose “Draw” and “Box” and then click the Draw button
  • Click on the map to start drawing a rectangle around your desired area
  • Then click Search
  • The right panel will show you all the different datasets available in that area
  • We want the QLD Government 1 Metre DEM, click the down arrow on the right
  • As you hover over the different options, they will highlight a red box on the map, select all that overlap the area you’re interested in (note that there may be data from different years here)
  • When you have the data you want, scroll to the bottom of the Order Data window
  • Select your industry, enter your email, tick the reCAPTCHA, and click the Order Datasets button
  • You should receive an email within 5 minutes, download the files from the link in the email, extract the folder to your project folder, and add them to your map.

Aerial Imagery

There are a few places you can aquire aerial photography, today we will look at two sources, one is freely available Government Data from QImagery, the other is accessible from using your UQ credentials.

  • Go to https://qimagery.information.qld.gov.au/
  • Read and tick the “I acknowledge I have read and agree to the Terms & Conditions” box, and click Get Started
  • Click the Search button, select ‘locality, town or city’ and search for “St Lucia” in the “Enter search term” search box and select the first result
  • It will zoom to your selected location then click the newly appeared Search button
  • From here you can select from a wide array of images of QLD over many years.
  • Click one of the drop-downs and hover over the options to see where those images are located. Preview the image by clicking View.
  • You can then download your desired images by clicking “Download” and selecting TIFF (georeferenced)
  • Move the TIFF file(s) to your project folder, and open them in QGIS

If you want even higher resolution maps, there are restricted options available. Your particular study area may have maps available such as the Sunshine Coast MyMaps service, CSIRO’s Norfolk Island Data Portal or other CSIRO spatial products. It’s worth exploring to discover what various local council and government resources are available. As a UQ student, you also have access to very high resoltuion imagery from NearMap. You can even access an array of imagery going back in time.

  • Go to the UQ NearMap Portal
  • Enter your UQ Student (@student.uq.edu.au) or Staff (@uq.edu.au) email address, with the appropriate domain selected. Click “Invite me”.
  • You should receive an email soon after, click the “Accept Invitation” button, and go through the account setup process.
  • Go to Login and enter your email address, click “Next” and enter your password.
  • From the top right select MapBrowser.
  • Type “St Lucia, QLD” in the search box, press enter
  • You can click the date down the bottom to look at different snapshots in time, and even compare maps side-by-side.
  • To save imagery from NearMap, simply click the “Exports” button on the left handside (it is an image icon)
  • From the menu that appears change the “Export type” to “Georeferenced image”
  • From “Projection” choose GDA2020 / MGA zone 56
  • You can increase and decrease the size of the bounding box by adjusting its corners, a smaller box means you can have a finer resolution, down to 0.075m. If we select all of UQ St Lucia in one go, the highest resolution we can have is 0.299m.
  • Once you’re happy with your selection click Download Files
  • Move the downloaded zip file to your project folder, and open them in QGIS

Lot Plans

You can access a wide variety of QLD Government Data, including Spatial Data such as lot plans and vegetation maps, from QLD Spatial. I will show you how to download the files, but the data is often quite large in size, so I have downloaded it beforehand, and trimmed the raw data down for you to download from our Github site.

  • To access data from QLD Spatial go to https://qldspatial.information.qld.gov.au/
  • Search for “property boundaries” and select the “property boundaries Queensland” option.
  • You could download this file, however, as it is the property boundaries for all of QLD, so you can find the trimmed file for our workshop here, just press the three dots and download.
  • Move the downloaded zip file to your project folder, and open the shapefile in QGIS

Queensland Globe

Another way to access QSpatial Data is using the Queensland Globe portal.

  • To access data from Queensland Globe go to https://qldglobe.information.qld.gov.au
  • Accept the T&Cs.
  • Click Search, Select Locality (Suburb) within a Local Government Area, and search for the location you want and select it from the list.
  • Click Layers, click Add Layers + here you can scroll through and filter different layer types
  • We want to tick the box next to Planning Cadastre > Land Parcels > Land Parcel (you may need to zoom in to see certain layers)
  • To export data click the Wrench Icon in the top right, and then click the Identify icon (i)
  • Use the triangular Identify Polygon tool to select and area of interest. Double click when you’ve finished selecting your area.
  • The Layers menu will now show your selection. You can download all, or sections, of your selection.
  • I will choose Land Parcel and then Download as a shp file.
  • Note: You may need to disable other layers for this to work correctly. I needed to turn off the Transportation layer to prevent roads from being included in my selection.

Import our data

If you have saved your data into your Data folder within your project folder qgis_mobile, it should appear in Project Home. You can import it into your project’s layers by double-clicking on the data there.

Create a buffer to clip our data

We now want to only keep data that is relevant to the St Lucia campus. To achieve that, we need a mask to clip data.

We first need to select the lots that are relevant by using the “Select Feature by area or single click” (in the toolbar), clicking on the lots one by one (or drawing a rectangle around them) with the Shift key pressed.

We can now create a buffer:

  • Go to Vector > Geoprocessing Tools > Buffer
  • Choose “Brisbane_lot_plans” as the Input Layer, and tick the Selected features only box
  • There are many settings we can change to edit the shape of the buffer, but let’s leave most of these as the defaults for now.
  • We can choose the distance that we want to create a buffer away from our vector. You’ll note that the distance is currently in degrees, as the layer projection is EPSG:4283 GDA94, a geographic coordinate system. This might cause issues.
  • If you click Run. Your buffer won’t look very good. We need to convert our layer to a local projected coordinate system.

Let’s reproject the layer for better results:

  • Go to Vector > Data Management Tools > Reproject Layer
  • Choose “Brisbane_lot_plans” as the Input Layer, and tick the Selected features only box
  • We want to choose a local projected coordinate system such as GDA94 / MGA zone 56 or GDA2020 / MGA zone 56. This will convert our measurements to metres instead of degrees, and by choosing an Australian projection, it reduces distortion.
  • Click “Run”
  • The new scratch layer will look the same, but it now has a different projection.

Let’s create that buffer again.

  • Select the relevant lots
  • Go to Vector > Geoprocessing Tools > Buffer
  • This time choose “Reprojected” as the Input Layer
  • You’ll notice the distance is now in metres. For this instance, I want a larger buffer of 50 m.
  • When you click “Run”, your buffer should be a good distance away from the original boundary.

Now we can Dissolve those polygons together:

  • Go to `Vector > Geoprocessing Tools > Dissolve
  • Choose “Buffered” as the Input Layer.
  • Let’s save this one to file, rather than a temporary file. Click “…” next to “[Create Temporary Layer]”, then “Save to file”, and save it as something like UQ Boundary to your project folder.

Note the Buffer tool has a “dissolve” option, but it’s important to know that there are many tools available.

Combine our DEMs

See the visible line between the raster tiles? That is because the separate raster files have different maximum and minimum values, so use different shades for different elevations. We have to merge them to make sure they use the same colour scale.

To do that, we use the Raster > Miscellaneous > Merge... tool to create one single layer from them.

  • First, select all DEM layers for the “Input layers”
  • Make sure the option “Place each input file into a separate band” is unchecked, as we want to end up with one single-band layer
  • We can save the output on disk instead of only creating a temporary file (for example, name it St_Lucia_DEM_merged and save it inside your project directory)
  • Click “Run”

You will need to have Saga installed for this to work.

We can now remove the original DEM raster files.

Clip the DEM

We now use Raster > Extraction > Clip Raster by Mask Layer to focus on our area of interest.

  • Make sure the virtual raster output DEM is selected in the Input layer

  • Set the Mask Layer to “UQ_Boundary”

  • Scroll down to “Clipped (mask)” and click “…” next to [Create Temporary Layer]“, then”Save to file”, and save it as St_Lucia_DEM to your project folder.

  • Another way to clip would be to use Extent

  • Make sure the virtual raster output DEM is selected in the Input layer

  • Navigate to Raster > Extraction > Clip Raster by Extent

  • Next to “Clipping extent” click ... > Calculate from Layer > UQ_Boundary

  • Scroll down to “Clipped (extent)” and click “…” next to [Create Temporary Layer]“, then”Save to file”, and save it as St_Lucia_DEM to your project folder.

If you don’t save to file directly, remember two things:

  • rename your clipped layer so it is more descriptive than the generic “Clipped (extent)”
  • you are currently using a temporary, scratch layer. It will be discarded if you exit QGIS. It is very useful for temporary intermediate files, but it can be safer to save copies of your intermediate data while you work, just in case! You can right-click on the layer and use Export > Save As..

Save your project

It’s not essential at this stage, it’s just a good reminder to save your work regularly so you don’t lose things when things go wrong.

Clip the Aerial Imagery

We can repeat the same process as above to clip the Aerial Imagery.

Now, clip the converted aerial imagery:

  • Go to Raster > Extraction > Clip Raster by Extent
  • Make sure St_Lucia_Aerial is selected in the Input layer
  • Set the Mask Layer to “UQ_Boundary”
  • You may need to define the Source and Target CRS to ensure that it all runs smoothly
  • Scroll down to “Clipped (mask)” and click “…” next to [Create Temporary Layer]“, then”Save to file”, and save it as St_Lucia_Aerial_clipped to your project folder.

We can now clean up our project by removing the original and intermediate layers we won’t need.

Change the symbology

We can style our DEM with a terrain colour palette:

  • double-click on the clipped DEM layer
  • go to the “Symbology” tab
  • change the Render type to “Singleband pseudocolor”
  • by default, it uses the min/max values, which is what we want
  • we can change the “Color ramp” to something more suitable with the drop-down menu and Create new color ramp... > Catalog: cpt-city > Topography > Elevation, for example.

Add a hillshade

Adding a hillshade makes your visualisation of elevation more readable and visually pleasing by giving an artificial lighting look to your map.

  • Go to Raster > Analysis > Hillshade....
  • Ensure the Input Layer is your clipped DEM “St_Lucia_DEM”
  • Scroll down to “Hillshade” and click “…” next to [Create Temporary Layer]“, then”Save to file”, and save it as St_Lucia_DEM_Hillshade to your project folder.
  • Click Run

Create Contours

Adding a contour makes your elevation even more evident and can also be used to quickly show elevation on other layers

  • Go to Raster > Extraction > Contour....
  • Ensure the Input Layer is your clipped DEM “St_Lucia_DEM”
  • For Interval between contour lines, the default is 10 m, which won’t be greatly noticeable at UQ where the highest point is 25 m. However, the finer the contour lines, the longer it will take to process. I will choose 5 m.
  • Scroll down to “Contours” and click “…” next to [Create Temporary Layer]“, then”Save to file”, and save it as St_Lucia_Contours_5m to your project folder.
  • Click Run

Exporting to Avenza Maps

Click on Show Layout Manager in the toolbar or use Project > Layout Manager. Create a new layout called “Avenza”. We can now see the Layout window.

Normally we would add many elements to our layout if we were exporting it for print such as the map, a legend, a scale bar, a north arrow…

In this case however, we are simply interested in our map. Let’s add the map to the canvas:

  • Go to the Layout tab, scroll down to ‘Resize Layout to Content’, click ‘Resize layout’
  • Before we export, let’s turn off any layers we aren’t using in QGIS to save space
  • Click the Refresh View button up the top
  • Now we are ready to export.
  • Go to ‘Layout > Export as PDF…’ and save your map.
  • The ‘PDF Export Options’ window will open
  • Tick the ‘Create Geospatial PDF (GeoPDF)’ box
  • Click ‘Save’

You can repeat this process with the DEM and Hillshade to export out another kind of map.

Now you simply need to export the pdf file(s) to your phone. You can email it, send it through the cloud, or transfer it using a cable.

When you first open Avenza Maps it will ask you to create an account, but you can import up to three maps without doing so, you can avoid creating an account by selecting the ‘x’ in the top right corner. * Allow Avenza Maps to access your device location * Select the orange ‘+’ in the bottom right and select ‘Download or import a map’ * Choose ‘From Storage Locations’ (if requested, give Avenza Maps the permissions to access your files) * Do the same for the other map, if you created one. * Once it has been imported, tap on the map. * You can now move the map around with your finger, and pinching to zoom. * Tapping the placemark icon in the bottom left will add a placemark in the middle of the crosshairs. * Tapping the 3 dots in the bottom right will allow you to add GPS tracking and draw and measure distances.

QField

QField is another Android based GIS app.