Creating a Country-Based Grid for openrouteservice

This tutorial explains how to prepare a country-based grid dataset for openrouteservice.

Step 1: Prepare the Country Data

1. Load your country dataset into QGIS.
2. If your data consists of multiple GeoJSON files, merge them into a single vector layer:
   • Go to Vector → Data Management Tools → Merge Vector Layers.
   • Under Input Layers, select all GeoJSON files.

Step 2: Create Grids

You will create two rectangular grids covering the same extent as your country layer.

1. Go to Vector → Research Tools → Create Grid.
2. For the first grid:
   • Grid type: Rectangle (Polygon)
   • Grid extent: Same as the country layer
   • Horizontal/Vertical spacing : 10 degrees
   • Grid: hierarchy grid
3. For the second grid:
   • Grid type: Rectangle (Polygon)
   • Grid extent: Same as the country layer
   • Horizontal/Vertical spacing: 1 degree
   • Grid: cell grid

Step 3: Assign Hierarchy IDs

Join the two grids so that each 1° cell knows which 10° cell it belongs to.

1. Go to Vector → Data Management Tools → Join Attributes by Location.
2. Set the parameters:
   • Base layer: cell grid
   • Join layer: hierarchy grid
   • Geometric predicate: intersect
3. Run the tool.
4. In the output, rename the joined field id_2 to hierarchy:
   • Right-click the layer → Properties → Fields → click the edit pencil and rename.

Step 4: Clip to Country Borders

1. Go to Vector → Geoprocessing Tools → Clip.

2. Set the parameters:

   • Input layer: grid created in the previous step
   • Overlay layer: country layer

3. Run the tool.

   • The output will be a grid clipped by country borders (some cells remain square, others follow borders).

Step 5: Combine Country Names and Grid Attributes

1. Go to Vector → Geoprocessing Tools → Union.
2. Set the parameters:
   • Input layer: the clipped grid
   • Overlay layer: the country layer
3. Run the union.
   • This step combines country names with hierarchy and cell IDs.
   • It may take some time depending on your dataset size.

The attribute table should now look like this:

id	hierarchy	NAME
1	1	Morocco
2	1	Morocco
3	2	Algeria
4	2	Algeria
5	3	Tunisia
6	3	Tunisia
7	4	Libya
8	4	Libya
9	5	Egypt
10	5	Egypt

Step 6: Export the Final Dataset

Export the final union layer as a GeoJSON file. When exporting, ensure that at least the following fields are included:

• name – country name
• hierarchy – hierarchy ID

This GeoJSON file can now be used within openrouteservice or related workflows.

Step 7 (optional): Manually merge inner country cells

By selecting and merging inner country cells, you can reduce the number of features in the final GeoJSON file.