How do you move a whole GeoJSON feature collection in QGIS?

As a software engineer working with geospatial data, I'm constantly creating or sourcing test data for my applications. If you want to have realistic tests, you need realistic data.

Good test data is time-consuming to create from scratch. You might have a perfect dataset, like a fire spread prediction in GeoJSON format for a region on the NSW/ACT border in Australia, but you need it to test a scenario for British Columbia in Canada.

How do you take a feature collection that's geographically anchored to one part of the world and simply move it to another?

While you could write a script to iterate over every coordinate, I find it easier to take the visual approach using QGIS. Lets look at using the Affine Transformation tool to translate your vector data to any location on the globe.

Reusing geographically locked data

Let's stick with our scenario. We have a GeoJSON file representing a hypothetical wildfire spread near Canberra, Australia. Our application needs to be tested for a similar scenario in the Canadian wilderness. The shape, complexity, and attributes of our Australian data are perfect, but its location is wrong.

The goal is to move the entire set of polygons from its source location to a new target destination without altering its shape or scale. This process is called translation, its a core geometric operation that the Affine Transformation tool in QGIS provides an interface for.

The solution: A two-step math problem

All we need to do is calculate the difference in longitude (the x-axis) and latitude (the y-axis) between our starting point and our destination. This difference, or "offset," is what we'll provide to QGIS.

Step 1: Find your source and target coordinates

First, you need to identify a reference point in both your source and target locations. This can be the centroid of your data, a specific city, or just a general point in the area of interest. For our example, let's use the following coordinates:

• Source Location (NSW/ACT Border, AU): 149.20576, -35.20385
• Target Location (British Columbia, CA): -120.7946, 54.7963

Step 2: Calculate the translation offset

Now, we perform a simple subtraction to find the distance we need to move our data along each axis. The formula is straightforward: Offset = Target Coordinate - Source Coordinate.

• X-axis Difference (Longitude): (-120.7946) - 149.20576 = -270.00036

• Y-axis Difference (Latitude): 54.7963 - (-35.20385) = 90.00015

These two numbers are all we need. The negative value for the x-axis tells QGIS to move the data to the west, and the positive value for the y-axis tells it to move the data to the north.

Applying the affine transformation in QGIS

With our offsets calculated, it's time to put them to work in QGIS.

1. Load Your Data: First, open QGIS and load your source vector layer (e.g., your fire prediction GeoJSON file). You should see it displayed in its original location in Australia.
2. Open the Affine Transformation Tool: In the top menu, go to Processing > Toolbox. In the Processing Toolbox panel that appears, search for "Affine" and double-click the Affine Transformation tool under the Vector geometry section.
3. Configure the Transformation: In the Affine Transformation window, you'll see several fields.
   • Input layer: Select your source GeoJSON layer from the dropdown.
   • Translation (x-axis): Enter the X-axis difference we calculated: -270.00036.
   • Translation (y-axis): Enter the Y-axis difference we calculated: 90.00015.
   • Scale (x-axis) & Scale (y-axis): Leave these as 1.0. We aren't resizing the data.
   • Rotation (z-axis): Leave this as 0.0. We aren't rotating the data.
   • Transformed: You can leave this as [Create temporary layer]. This allows you to preview the result before saving it permanently.
4. Run the Tool: Click the Run button.

QGIS will instantly perform the calculation on every vertex in your layer and generate a new temporary layer named "Transformed." If you zoom to the target coordinates in Canada, you will see your data sitting perfectly in its new home.

Save your new layer

The temporary layer only exists for your current QGIS session. To make it permanent, right-click on the Transformed layer in the Layers panel, go to Export > Save Features As..., and save it in your desired format, such as GeoJSON.

We've successfully moved a complex geospatial dataset across the world without writing a single line of code.

The Affine Transformation tool is a great way to handle this classic data prep task, allowing you to repurpose test data for different geographic contexts and immediately inspect the results visually.