[DefaultValue(null)]
public IMapDataAdapter Data { get; set; }

<DefaultValue(Nothing)>
Public Property Data As IMapDataAdapter

using System;
using System.Windows.Forms;
using DevExpress.XtraMap;

namespace AddItemsManually {

    public partial class Form1 : Form {

        public Form1() {
            InitializeComponent();
        }

        private void Form1_Load(object sender, EventArgs e) {
            // Create a map control with initial settings and add it to the form.
            MapControl map = new MapControl() 
                             { Dock = DockStyle.Fill, ZoomLevel = 4, CenterPoint = new GeoPoint(43, 15) };
            this.Controls.Add(map);

            // Create a layer to load image tiles from OpenStreetMap.
            ImageLayer tileLayer = new ImageLayer();
            tileLayer.DataProvider = new OpenStreetMapDataProvider();
            map.Layers.Add(tileLayer);

            // Create a layer to display vector items.
            VectorItemsLayer itemsLayer = new VectorItemsLayer();
            map.Layers.Add(itemsLayer);

            // Create a storage for map items and generate them.
            MapItemStorage storage = new MapItemStorage();
            MapItem[] capitals = GetCapitals();
            storage.Items.AddRange(capitals);
            itemsLayer.Data = storage;
        }

        // Create an array of callouts for 5 capital cities.
        MapItem[] GetCapitals() {
            return new MapItem[] { 
                new MapCallout() { Text = "London", Location = new GeoPoint(51.507222, -0.1275) },
                new MapCallout() { Text = "Rome", Location = new GeoPoint(41.9, 12.5) },
                new MapCallout() { Text = "Paris", Location = new GeoPoint(48.8567, 2.3508) },
                new MapCallout() { Text = "Berlin", Location = new GeoPoint(52.52, 13.38) },
                new MapCallout() { Text = "Madrid", Location = new GeoPoint(40.4, -3.68) }
            };
        }
    }

}

Imports System
Imports System.Windows.Forms
Imports DevExpress.XtraMap

Namespace AddItemsManually

    Partial Public Class Form1
        Inherits Form

        Public Sub New()
            InitializeComponent()
        End Sub

        Private Sub Form1_Load(ByVal sender As Object, ByVal e As EventArgs) Handles MyBase.Load
            ' Create a map control with initial settings and add it to the form.
            Dim map As New MapControl() With {.Dock = DockStyle.Fill, .ZoomLevel = 4, .CenterPoint = New GeoPoint(43, 15)}
            Me.Controls.Add(map)

            ' Create a layer to load image tiles from OpenStreetMap.
            Dim tileLayer As New ImageLayer()
            tileLayer.DataProvider = New OpenStreetMapDataProvider()
            map.Layers.Add(tileLayer)

            ' Create a layer to display vector items.
            Dim itemsLayer As New VectorItemsLayer()
            map.Layers.Add(itemsLayer)

            ' Create a storage for map items and generate them.
            Dim storage As New MapItemStorage()
            Dim capitals() As MapItem = GetCapitals()
            storage.Items.AddRange(capitals)
            itemsLayer.Data = storage
        End Sub

        ' Create an array of callouts for 5 capital cities.
        Private Function GetCapitals() As MapItem()
            Return New MapItem() { _
                New MapCallout() With {.Text = "London", .Location = New GeoPoint(51.507222, -0.1275)}, _
                New MapCallout() With {.Text = "Rome", .Location = New GeoPoint(41.9, 12.5)}, _
                New MapCallout() With {.Text = "Paris", .Location = New GeoPoint(48.8567, 2.3508)}, _
                New MapCallout() With {.Text = "Berlin", .Location = New GeoPoint(52.52, 13.38)}, _
                New MapCallout() With {.Text = "Madrid", .Location = New GeoPoint(40.4, -3.68)} _
            }
        End Function
    End Class

End Namespace

// Create data for the MapLayer.
MapLayer.Data = CreateData();
#endregion #DataProperty

Adapter = new ShapefileDataAdapter();
vectorLayer.Data = Adapter;
vectorLayer.DataLoaded += DataLayer_DataLoaded;

Uri baseUri = new Uri(System.Reflection.Assembly.GetEntryAssembly().Location);
KmlLayer.Data = new KmlFileDataAdapter() {
    FileUri = new Uri(baseUri, filePath)

storage.Items.AddRange(capitals);
    itemsLayer.Data = storage;
}

VectorItemsLayer items = new VectorItemsLayer();
items.Data = new MapItemStorage();
map.Layers.Add(items);

' Create data for the MapLayer.
            Me.MapLayer.Data = Me.CreateData()
'#End Region ' #DataProperty

Adapter = New ShapefileDataAdapter()
vectorLayer.Data = Adapter
AddHandler vectorLayer.DataLoaded, AddressOf DataLayer_DataLoaded

Dim baseUri As Uri = New Uri(Reflection.Assembly.GetEntryAssembly().Location)
            KmlLayer.Data = New KmlFileDataAdapter() With {.FileUri = New Uri(baseUri, filePath)}
'#End Region ' #KmlFileDataAdapter

storage.Items.AddRange(capitals)
    itemsLayer.Data = storage
End Sub

Dim items As VectorItemsLayer = New VectorItemsLayer()
items.Data = New MapItemStorage()
map.Layers.Add(items)