原理
在API中，使用ArcGISTileMapServiceLayer 来加载瓦片地图，除了天地图之外，GOOGLE和BING的地图也采用这种方法进行加载。使用该地图类型加载，需要对几个地方进行修改：
1、空间坐标系（this.spatialReference）
2、地图范围（this.initialExtent）
3、瓦片地图信息（this.tileInfo），这里需要对 esri.layers.TileInfo进行定义。其中包括了瓦片行列的数量（"rows“，“clos”），坐标系("spatialreference")，不同等级的比例尺（"lods"）
4.重写getTileUrl方法，以便API正确的获取所需的瓦片。
天地图分析（转载自http://www.giser.net/?p=119）
天地图是中国区域内数据资源最全的地理信息服务网站，同时将为公众提供权威、可信、统一的地理信息服务，在我国的公共服务平台建设中将起到重要作用，那么为了在其他系统中使用天地图的地图服务，就很有必要对天地图的切图schema研究一番。
下面就把天地图切图schema的主要参数列举一下：
1 参考系 ：wgs84 （4326）
2 切图原点（－180，90）
3 切图范围（－180，－90，180，90）
4 切图级别18级，比例尺和分辨率分别为：
{“level” : 1, “resolution” : 0.3515625, “scale” : 147748799.285417},
{“level” : 2, “resolution” : 0.17578125, “scale” : 73874399.6427087},
{“level” : 3, “resolution” : 0.087890625, “scale” : 36937199.8213544},
{“level” : 4, “resolution” : 0.0439453125, “scale” : 18468599.9106772},
{“level” : 5, “resolution” : 0.02197265625, “scale” : 9234299.95533859},
{“level” : 6, “resolution” : 0.010986328125, “scale” : 4617149.97766929},
{“level” : 7, “resolution” : 0.0054931640625, “scale” : 2308574.98883465},
{“level” : 8, “resolution” : 0.00274658203125, “scale” : 1154287.49441732},
{“level” : 9, “resolution” : 0.001373291015625, “scale” : 577143.747208662},
{“level” : 10, “resolution” : 0.0006866455078125, “scale” : 288571.873604331},
{“level” : 11, “resolution” : 0.00034332275390625, “scale” : 144285.936802165},
{“level” : 12, “resolution” : 0.000171661376953125, “scale” : 72142.9684010827},
{“level” : 13, “resolution” : 8.58306884765629E-05, “scale” : 36071.4842005414},
{“level” : 14, “resolution” : 4.29153442382814E-05, “scale” : 18035.7421002707},
{“level” : 15, “resolution” : 2.14576721191407E-05, “scale” : 9017.87105013534},
{“level” : 16, “resolution” : 1.07288360595703E-05, “scale” : 4508.93552506767},
{“level” : 17, “resolution” : 5.36441802978515E-06, “scale” : 2254.467762533835},
{“level” : 18, “resolution” : 2.68220901489258E-06, “scale” : 1127.2338812669175}
5 切图参数：
格式：png
大小：256＊256
dpi：96
6 服务器个数：8个，分别为：
http://tile0.tianditu.com/
http://tile1.tianditu.com/
http://tile2.tianditu.com/
http://tile3.tianditu.com/
http://tile4.tianditu.com/
http://tile5.tianditu.com/
http://tile6.tianditu.com/
http://tile7.tianditu.com/
7 切片请求方式：REST
8 切片请求地址http://tile0.tianditu.com/DataServer?T=AB0512_Anno&X=1&Y=0&L=2
其中x为列数，y为行数，l为级别
代码（转载自http://www.cnblogs.com/gisvip/archive/2012/03/25/2417229.html）
dojo.declare("TDTLayer", esri.layers.TiledMapServiceLayer, {
constructor: function() {
this.spatialReference = new esri.SpatialReference({ wkid:4326 });
this.initialExtent = (this.fullExtent = new esri.geometry.Extent(-180.0, -90.0, 180.0, 90.0, this.spatialReference));
this.tileInfo = new esri.layers.TileInfo({
"rows" : 256,
"cols" : 256,
"compressionQuality" : 0,
"origin" : {
"x" : -180,
"y" : 90
},
"spatialReference" : {
"wkid" : 4326
},
"lods" : [
{"level" : 0, "resolution" : 0.703125, "scale" : 295497593.05875003},
{"level" : 1, "resolution" : 0.3515625, "scale" : 147748796.52937502},
{"level" : 2, "resolution" : 0.17578125, "scale" : 73874398.264687508},
{"level" : 3, "resolution" : 0.087890625, "scale" : 36937199.132343754},
{"level" : 4, "resolution" : 0.0439453125, "scale" : 18468599.566171877},
{"level" : 5, "resolution" : 0.02197265625, "scale" : 9234299.7830859385},
{"level" : 6, "resolution" : 0.010986328125, "scale" : 4617149.8915429693},
{"level" : 7, "resolution" : 0.0054931640625, "scale" : 2308574.9457714846},
{"level" : 8, "resolution" : 0.00274658203125, "scale" : 1154287.4728857423},
{"level" : 9, "resolution" : 0.001373291015625, "scale" : 577143.73644287116},
{"level" : 10, "resolution" : 0.0006866455078125, "scale" : 288571.86822143558},
{"level" : 11, "resolution" : 0.00034332275390625, "scale" : 144285.93411071779},
{"level" : 12, "resolution" : 0.000171661376953125, "scale" : 72142.967055358895},
{"level" : 13, "resolution" : 8.58306884765625e-005, "scale" : 36071.483527679447},
{"level" : 14, "resolution" : 4.291534423828125e-005, "scale" : 18035.741763839724},
{"level" : 15, "resolution" : 2.1457672119140625e-005, "scale" : 9017.8708819198619},
{"level" : 16, "resolution" : 1.0728836059570313e-005, "scale" : 4508.9354409599309},
{"level" : 17, "resolution" : 5.3644180297851563e-006, "scale" : 2254.4677204799655}
]
});
this.loaded = true;
this.onLoad(this);
},
getTileUrl: function(level, row, col) {
var levelMap = "";
if(level<10){
levelMap = "A0512_EMap";
}else if(level<12){
levelMap = "B0627_EMap1112";
}else if(level<17){
levelMap = "siwei0608";
}
return "http://tile0.tianditu.com/DataServer?T="+levelMap+"&"+
"X=" + col + "&" +
"Y=" + row + "&" +
"L=" + (level*1+1);
}
});
dojo.declare("TDTAnnoLayer", esri.layers.TiledMapServiceLayer, {
constructor: function() {
this.spatialReference = new esri.SpatialReference({ wkid:4326 });
this.initialExtent = (this.fullExtent = new esri.geometry.Extent(-180.0, -90.0, 180.0, 90.0, this.spatialReference));
this.tileInfo = new esri.layers.TileInfo({
"rows" : 256,
"cols" : 256,
"compressionQuality" : 0,
"origin" : {
"x" : -180,
"y" : 90
},
"spatialReference" : {
"wkid" : 4326
},
"lods" : [
{"level" : 0, "resolution" : 0.703125, "scale" : 295497593.05875003},
{"level" : 1, "resolution" : 0.3515625, "scale" : 147748796.52937502},
{"level" : 2, "resolution" : 0.17578125, "scale" : 73874398.264687508},
{"level" : 3, "resolution" : 0.087890625, "scale" : 36937199.132343754},
{"level" : 4, "resolution" : 0.0439453125, "scale" : 18468599.566171877},
{"level" : 5, "resolution" : 0.02197265625, "scale" : 9234299.7830859385},
{"level" : 6, "resolution" : 0.010986328125, "scale" : 4617149.8915429693},
{"level" : 7, "resolution" : 0.0054931640625, "scale" : 2308574.9457714846},
{"level" : 8, "resolution" : 0.00274658203125, "scale" : 1154287.4728857423},
{"level" : 9, "resolution" : 0.001373291015625, "scale" : 577143.73644287116},
{"level" : 10, "resolution" : 0.0006866455078125, "scale" : 288571.86822143558},
{"level" : 11, "resolution" : 0.00034332275390625, "scale" : 144285.93411071779},
{"level" : 12, "resolution" : 0.000171661376953125, "scale" : 72142.967055358895},
{"level" : 13, "resolution" : 8.58306884765625e-005, "scale" : 36071.483527679447},
{"level" : 14, "resolution" : 4.291534423828125e-005, "scale" : 18035.741763839724},
{"level" : 15, "resolution" : 2.1457672119140625e-005, "scale" : 9017.8708819198619},
{"level" : 16, "resolution" : 1.0728836059570313e-005, "scale" : 4508.9354409599309},
{"level" : 17, "resolution" : 5.3644180297851563e-006, "scale" : 2254.4677204799655}
]
});
this.loaded = true;
this.onLoad(this);
},
getTileUrl: function(level, row, col) {
return "http://tile0.tianditu.com/DataServer?T=AB0512_Anno&"+
"X=" + col + "&" +
"Y=" + row + "&" +
"L=" + (level*1+1);
}
});