HelloMap.cs

using System;
using System.Threading.Tasks;
using Plugin.Geolocator;
using Xamarin.Forms;
using Xamarin.Forms.Maps;

namespace HelloMap
{
	public class App : Application
	{
		Map map;
		public App()
		{

			map = new Map(
				MapSpan.FromCenterAndRadius( // 描画対象の範囲の生成
					new Position(39.7021981, 141.1305283), // 中央位置 
					Distance.FromKilometers(2))) // 中央位置からの距離
			{
				IsShowingUser = true, // 現在の位置情報の描画
				HeightRequest = 200, // 高さ（ピクセル）
				WidthRequest = 960, // 幅（ピクセル）
				VerticalOptions = LayoutOptions.FillAndExpand
			};

			// The root page of your application
			var content = new ContentPage
			{
				Title = "HelloMap",
				Content = new StackLayout
				{
					VerticalOptions = LayoutOptions.Center,
					Children = {
						new Label {
							HorizontalTextAlignment = TextAlignment.Center,
							Text = "Welcome to Xamarin FormsMaps!"
						},
						map // 地図の描画
					}
				}
			};			 

			MainPage = new NavigationPage(content);
		}

		protected override void OnStart()
		{
			// Handle when your app starts
			updateLocation();
		}

		// update location
		public async Task updateLocation()
		{
			var locator = CrossGeolocator.Current;
			var position = await locator.GetPositionAsync(timeoutMilliseconds: 10000);
			map.MoveToRegion(
				MapSpan.FromCenterAndRadius(
				new Position(position.Latitude, position.Longitude), 
					Distance.FromKilometers(1)));
		}

		protected override void OnSleep()
		{
			// Handle when your app sleeps
		}

		protected override void OnResume()
		{
			// Handle when your app resumes
		}
	}
}