Extended GeoJSON geometries

Artikkel
04/13/2023

Azure Maps provides a list of powerful APIs to search inside and along geographical features. These APIs adhere to the standard GeoJSON spec of representing geographical features.

The GeoJSON spec supports only the following geometries:

GeometryCollection
LineString
MultiLineString
MultiPoint
MultiPolygon
Point
Polygon

Some Azure Maps APIs accept geometries that aren't part of the GeoJSON spec. For instance, the Search Inside Geometry API accepts Circle and Polygons.

This article provides a detailed explanation on how Azure Maps extends the GeoJSON spec to represent certain geometries.

Circle

The GeoJSON spec doesn't support the Circle geometry. The GeoJSON Point Feature object is used to represent a circle.

A Circle geometry represented using the GeoJSON Feature object must contain the following coordinates and properties:

Coordinate	Property
Center	The circle's center is represented using a `GeoJSON Point` object.
Radius	The circle's `radius` is represented using `GeoJSON Feature`'s properties. The radius value is in meters and must be of the type `double`.
SubType	The circle geometry must also contain the `subType` property. This property must be a part of the `GeoJSON Feature`'s properties and its value should be Circle

Circle example

Here's how you represent a circle using a GeoJSON Feature object. Let's center the circle at latitude: 47.639754 and longitude: -122.126986, and assign it a radius equal to 100 meters:

{
    "type": "Feature",
    "geometry": {
        "type": "Point",
        "coordinates": [-122.126986, 47.639754]
    },
    "properties": {
        "subType": "Circle",
        "radius": 100
    }
}

Rectangle

The GeoJSON spec doesn't support the Rectangle geometry. The GeoJSON Polygon Feature object is used to represent a rectangle. The rectangle extension is primarily used by the Web SDK's drawing tools module.

A Rectangle geometry represented using the GeoJSON Polygon Feature object must contain the following coordinates and properties:

Coordinate	Property
Corners	The rectangle's corners are represented using the coordinates of a `GeoJSON Polygon` object. There should be five coordinates, one for each corner. And, a fifth coordinate that is the same as the first coordinate, to close the polygon ring. It's assumed that these coordinates align, and that the developer may rotate them as wanted.
SubType	The rectangle geometry must also contain the `subType` property. This property must be a part of the `GeoJSON Feature`'s properties, and its value should be Rectangle.

Rectangle example

{
    "type": "Feature",
    "geometry": {
        "type": "Polygon",
        "coordinates": [[[5,25],[14,25],[14,29],[5,29],[5,25]]]
    },
    "properties": {
        "subType": "Rectangle"
    }
}

Next steps

Learn more about GeoJSON data in Azure Maps:

Geofence GeoJSON format

Review the glossary of common technical terms associated with Azure Maps and location intelligence applications:

Azure Maps glossary

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