Dear Ken,
Below I am posting my code.Kindly refer it.
<!DOCTYPE html>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<meta name="viewport" content="initial-scale=1, maximum-scale=1,user-scalable=no"/>
<title>Simple Map</title>
<link rel="stylesheet" href="https://js.arcgis.com/3.25/esri/css/esri.css">
<style>
html, body, #map {
height: 100%;
margin: 0;
padding: 0;
}
</style>
<script src="https://js.arcgis.com/3.25/"></script>
<script>
var map;
require(["esri/map","esri/dijit/Basemap",
"esri/dijit/BasemapLayer", "dojo/domReady!"], function(Map,Basemap, BasemapLayer) {
var lyrGEBCO = new BasemapLayer(
{ url : "https://maps.ngdc.noaa.gov/arcgis/rest/services/web_mercator/gebco_2014_hillshade/MapServer"
//url : "https://services.arcgisonline.com/ArcGIS/rest/services/World_Topo_Map/MapServer"
});
var bmapGEBCO = new Basemap ({ layers : [ lyrGEBCO ],
title : "GEBCO",
thumbnailUrl : "images/mgs_gebco.png"
});
map = new Map("map", {
basemap: bmapGEBCO, //For full list of pre-defined basemaps, navigate to http://arcg.is/1JVo6Wd
center: [-122.45, 37.75], // longitude, latitude
zoom: 13
});
});
</script>
</head>
<body>
<div id="map"></div>
</body>
</html>
Regards,
Kishore Kumar