How to create an interest area GeoJSON

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For some calculation models, often those found in Project Templates, the actual area of interest to consider results of does extent across the entire extent of a Project. Instead, only a specific polygon may be relevant. This polygon is known as Interest Area. While creating a new Project, it is also possible to use a file defining such an area to automatically select the appropriate location and extent for the new Project. However, this relies on having a GeoJSON file with such a definition before starting work on a Project.

These steps describe the process in QGIS, but similar steps in other GIS applications can yield the same result.

How to create an interest area GeoJSON:
  1. Open a new or existing project in QGIS.
  2. Ensure some background layer exists, so that its possible to know where new features are drawn.
  3. Move the view to the location where the Interest Area is to be located.
  4. In the top menu, select Layer → Create Layer → New Temporary Scratch Layer
  5. Set the Name to "Interest Area", set Geometry Type to Polygon, and click "Ok"
  6. Use the Add Polygon Feature to draw a polygon in the correct location. Ensure it fits the area of interest as exactly as possible.
  7. Right-click the layer in the "Layers" list, and select Export → Save Features As
  8. Set the Format to GeoJSON.
  9. At the input for the File Name, select the location to save the GeoJSON file to.
  10. At the CRS, select an appropriate CRS.
  11. Click "OK" to complete the export.
  12. A GeoJSON file with a polygon defining the Interest Area has now been created.

Notes

  • Multiple discrete features may be present in a single Interest Area GeoJSON. Each feature will be loaded in as a separate Area.
    • When using MultiPolygons, each feature consisting of multiple Polygons will be loaded in as a single Area with multiple polygons.
  • No Attributes need to be added to the features. Attributes of the features in the GeoJSON file will be ignored when using it during Project generation. Instead, a single INTEREST_AREA Attribute with a value of "1" will be added to each of the Areas added in this way.
  • In The Netherlands, using Open Basis Kaart (https://www.openbasiskaart.nl/mapcache) as a WMS is a good way to obtain a background layer.
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