MainWindow.xaml.cs

using System;
using System.Globalization;
using System.Net;
using System.Windows;
using DevExpress.Xpf.Map;

namespace CustomMapDataProviderApp {

    public partial class MainWindow : Window {
        public MainWindow () {
            InitializeComponent();
            ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls12;
            CustomMapDataProvider provider = new CustomMapDataProvider();
            imageLayer.DataProvider = provider;
            provider.WebRequest += Provider_WebRequest;
        }

        private void Provider_WebRequest(object sender, MapWebRequestEventArgs e) {
            e.UserAgent = "Test Map App";
        }
    }

    public class CustomMapDataProvider : MapDataProviderBase {
        readonly SphericalMercatorProjection projection = new SphericalMercatorProjection();

        public override ProjectionBase Projection { get { return projection; } }

        public CustomMapDataProvider () {
            SetTileSource(new CustomTileSource());
        }
        protected override MapDependencyObject CreateObject () {
            return new CustomMapDataProvider();
        }
        public override Size GetMapSizeInPixels (double zoomLevel) {
            return new Size(Math.Pow(2.0, zoomLevel) * OpenStreetMapTileSource.tileSize, 
                Math.Pow(2.0, zoomLevel) * OpenStreetMapTileSource.tileSize);
        }
    }

    public class CustomTileSource : MapTileSourceBase {
        const string roadUrlTemplate = 
            @"http://{subdomain}.tile.openstreetmap.org/{tileLevel}/{tileX}/{tileY}.png";
        public const int maxZoomLevel = 20;
        public const int tileSize = 256;

        static int imageWidth = (int)Math.Pow(2.0, maxZoomLevel) * tileSize;
        static int imageHeight = (int)Math.Pow(2.0, maxZoomLevel) * tileSize;
        static string[] subdomains = new string[] { "a", "b", "c" };

        public CustomTileSource ()
            : base(imageWidth, imageHeight, tileSize, tileSize) {

        }
        public override Uri GetTileByZoomLevel (int zoomLevel, long tilePositionX, long tilePositionY) {
            string url = roadUrlTemplate;
            url = url.Replace("{tileX}", tilePositionX.ToString(CultureInfo.InvariantCulture));
            url = url.Replace("{tileY}", tilePositionY.ToString(CultureInfo.InvariantCulture));
            url = url.Replace("{tileLevel}", zoomLevel.ToString(CultureInfo.InvariantCulture));
            url = url.Replace("{subdomain}", subdomains[GetSubdomainIndex(subdomains.Length)]);
            return new Uri(url);
        }
    }
}