GeoJSON

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GeoJSON is the JSON format of web maps. GeoJson.Read and GeoJson.Parse read a FeatureCollection, a Feature or a geometry, and GeoJson.Write and GeoJson.Format write a FeatureCollection:

GeoFeatureCollection countries;
using (var stream = File.OpenRead("countries.geojson"))
{
    countries = GeoJson.Read(stream);
}

// A JSON number is a double, and a string is a string
var large = countries.Where(country => (double)country.Properties["population"]! > 50).ToList();
Assert.Equal("France", Assert.Single(large).Properties["name"]);

using (var stream = File.Create("large-countries.geojson"))
{
    GeoJson.Write(new GeoFeatureCollection(large), stream, new GeoJsonWriterOptions { Indented = true });
}

ParseGeometry and FormatGeometry read and write a single geometry.

What the reader keeps

The seven geometry types, with their altitudes.
The name of a FeatureCollection, as Name. The bbox and the other members that GeoJSON does not define are ignored.
The properties: a JSON string is a string, a number a double, true and false a bool, null is null, and an object or an array is a JsonElement.
The id: a string, or the JSON text of a number (42).

Options of the writer

GeoJsonWriterOptions sets:

Indented: indent the JSON.
WriteBoundingBoxes: add a bbox to the collection, the features and the geometries.

The writer writes the identifiers as strings, the numbers as JSON numbers (null when they are not finite), a JsonElement as it is, a dictionary as an object, a collection as an array, and the other values, such as dates, as their text. Only the characters JSON requires are escaped, so names in other scripts stay readable.