Requirement

Guidance

The geographical extent of the information can be expressed in various ways. For example it may concern a single ICAO Region (see ICAO Regions). However, it is also possible that it covers a combination of FIRs, ICAO Regions and aerodromes. Furthermore it is possible that the information covers the entire world.

Bounding Box

The use of the geographical bounding box raises special concerns.

• The service description information supports the discovery and assessment of services based on the geographical extent of the exchanged information.
• The geographical extent in a service description may be in a different coordinate reference system from the information that is exchanged by the service. 
• The GeoJSON standard uses the World Geodetic System 1984 (WGS 84) [WGS84] datum, with longitude and latitude units of decimal degrees. This means that the longitude appears before latitude in the position. However, it is customary in ATM to have latitude before longitude - therefore, users need to be aware of this difference.
• Translation to other coordinate reference systems may need to take place if a system is to understand the geographical extent correctly. There are established tools and software libraries for this so we need not worry as long as the input is clear.
• When encoding the polygons:
  • encode positions of the exterior  boundary counter-clockwise and any interior boundary clockwise. (That's how it is done in GML for aviation data guidance).
  • it is assumed that the x, y coordinates are captured in the polygon and altitude (z) coordinates are covered in the two altitude properties.

Note: The geoJSON standardisation group is considering the support for different coordinate reference systems. However, at the moment it only supports the World Geodetic System 1984 (WGS 84) [WGS84] datum, with longitude and latitude units of decimal degrees.

Verification Support

Examples

The following example shows the content as a table.

The following example shows an extract of the content of a JSON file that conforms to the Service Metadata Schema. It shows the use of an aerodrome location indicator and is supplemented by a geometry.

"serviceCategorisation": {
 ...
 "geospatialCategorisation": {
  "aerodrome": ["EADD"],
  "geometry": {
   "type": "GeometryCollection",
   "geometries": [{
    "type": "Point",
    "coordinates": [100.0, 0.0]
   }
  }
 }
}

The following example is where the information is worldwide.

"serviceCategorisation": {
 ...
 "geospatialCategorisation": {
  "description": "Worldwide."
 }
}

The following example is for an ICAO region using the value published at https://reference.swim.aero/information-services/service-categories/CodeICAORegionType.html#EUR.

"serviceCategorisation": {
 ...
 "geospatialCategorisation": {
  "region": ["EUR"]
 }
}

Complete examples are available at Example service description.