using System;

using System.Data;

using System.Linq;

using Newtonsoft.Json.Linq;

public class Program

{

    public static void Main()

    {

        DataSet GeoDS = GetDataSet();

        var obj = JObject.FromObject(GeoDS);

        obj["records"] = new JArray(obj["records"].Select(jo => new JObject(new JProperty("attributes", jo))));

        string json = obj.ToString();

​

        Console.WriteLine(json);

    }

    private static DataSet GetDataSet()

    {

        DataTable dt = new DataTable("records");

        dt.Columns.Add("OBJECTID");

        dt.Columns.Add("Address");

        dt.Columns.Add("City");

        dt.Columns.Add("Region");

        dt.Columns.Add("Postal");

        dt.Rows.Add(1, "4550 Cobb Parkway North NW", "Acworth", "GA", "30101");

        dt.Rows.Add(2, "2450 Old Milton Parkway", "Alpharetta", "GA", "30009");

        DataSet ds = new DataSet();

        ds.Tables.Add(dt);

        return ds;

    }

}