Designing a map to overlay ArcGIS Online services

If you'll be using the ArcGIS JavaScript API or the Web ADF to overlay your map on ArcGIS Online services, follow this workflow when you create your map:

Determine the tiling scheme of the service you will overlay

In December of 2009, ArcGIS Online began offering its services in the same coordinate system and tiling scheme used by Bing Maps and Google Maps. The previous services will continue to remain available for a time period in the "traditional" ArcGIS Online tiling scheme. At ArcGIS 9.4 the traditional ArcGIS Online tiling scheme will be retired, meaning you will no longer be able to select it as an option when creating a cache.

The first thing you need to do when designing a map to overlay ArcGIS Online is to determine which tiling scheme is used by the ArcGIS Online service you want to overlay. New maps and applications should attempt to overlay one of the services in the Bing Maps/Google Maps tiling scheme. However, when supporting legacy applications in may be necessary to create caches in the traditional ArcGIS Online tiling scheme.

If you are in doubt about whether the service you want to overlay uses the Bing/Google tiling scheme or the traditional ArcGIS Online tiling scheme, check the service's metadata page at http://resources.esri.com/arcgisonlineservices. Click "Data", then find the service you will overlay. If it is in the Retiring Maps section, uses the geographic coordinate system, is suffixed with "_2D", or is otherwise marked as retired, then it probably uses the traditional ArcGIS Online tiling scheme. Otherwise it uses the Bing Maps/Google Maps tiling scheme.

Overlaying an ArcGIS Online service in the Bing Maps/Google Maps tiling scheme

If the ArcGIS Online service you want to overlay uses the Bing Maps/Google Maps tiling scheme, you can often follow the instructions in Designing a map to overlay Google Maps or Bing Maps with success. However, if you'll be using the Web ADF to overlay the caches (includes applications built with Manager), or if your source data uses a datum other than WGS 84 or NAD 83, do the following instead:

1. Open your source map document in ArcMap and set your data frame coordinate system to WGS 1984 Web Mercator (Auxiliary Sphere). While you are doing this, apply any datum transformations to WGS 1984 that you require.
2. Follow the steps in ESRI Knowledge Base Article 37329 to build your cache.

Technical note: The above two steps are helpful in some cases because the ArcGIS Online services in the Bing Maps/Google Maps tiling scheme are published with a different coordinate system well-known ID (102100) than the well-known ID required by ArcCatalog 9.3.1 when you choose the Microsoft Virtual Earth/Google Maps tiling scheme (102113). The coordinate systems are mathematically equivalent and there is no visual difference between the tiles, but some clients such as the Web ADF require an exact match of well-known ID. Also, datum transformations are easier to apply in ArcMap when 102100 is used. The ArcGIS Online help topic Migrating map tiling schemes contains more detail about this issue.

Overlaying an ArcGIS Online service in the "traditional" ArcGIS Online tiling scheme

If the service you want to overlay uses the "traditional" ArcGIS Online tiling scheme based on the WGS 1984 geographic coordinate system, continue reading the article below to learn how to design a map to overlay the service. Note that these services will not undergo further updates and you should consider a migration path for your applications to use ArcGIS Online services in the Bing Maps/Google Maps tiling scheme.

Author the map

You'll originally create the map in ArcMap by adding data and symbolizing it appropriately. When designing the map, you need to use the same coordinate system and scales used by ArcGIS Online services.

Change the coordinate system to WGS 1984

The first thing you should do when designing the map is change the coordinate system to the same one used by ArcGIS Online services, which is WGS 1984. To change the coordinate system, follow these steps:

1. Right-click the data frame name in the ArcMap table of contents (Layers by default) and click Properties.
2. Click the Coordinate System tab.
3. Click Predefined > Geographic Coordinate Systems > World > WGS 1984, then click OK.

Design at the ArcGIS Online scales

Users of your map will see it at the scales used by ArcGIS Online services, so you should only design your map at those scales. But how do you know what those scales are?

You can load the ArcGIS Online scales into the ArcMap scale drop-down list by doing the following:

1. Copy this text file arcgis_online_scales.txt to a location that you can easily remember. (The link here is provided for simplicity. The file is originally installed in the Help directory of your ArcGIS Server instance. Example: C:\Inetpub\wwwroot\ArcGIS\Manager\Help\arcgis_online_scales.txt)
2. Open ArcMap and add some data.
3. Click the dropdown list of scales and click Customize This List.
4. Click Load.
5. Browse to the arcgis_online_scales.txt file mentioned in Step 1 and click Open.
6. Click OK to apply your changes and dismiss the dialog. You should now be able to see all of the ArcGIS Online scales and easily jump between them using the dropdown.

You only need to design your map to look good at the scales at which it will be cached. If you do not plan on caching your map at the larger scales, you do not need to do any design work at those scales.

Set scale ranges on your layers so that just the right amount of data and labels are visible at each scale, symbolized appropriately. When setting your scale ranges, avoid toggling layers on and off at or near the scales at which you are designing.

You may need to make copies of your layers so that you can symbolize them differently at various scales. The ArcMap table of contents can contain multiple copies of a layer, each with its own symbology and scale ranges. To copy a layer, right-click it in the ArcMap table of contents and click Copy. Then right-click the data frame name and click Paste Layer(s).

Publish the map as a service

After you've finished authoring your map document (.mxd), you need to publish it as an ArcGIS Server map service before you can use it in your application. One of the easiest ways to do this is to right-click the map document in ArcCatalog and click Publish to ArcGIS Server.

Learn more about publishing a GIS resource to the server.

Create a map cache

One of the reasons ArcGIS Online services are so fast is that they use server-side map caching, meaning that predrawn images of the map are stored on the server so that you can quickly request them through a URL. With ArcGIS Server, you can create a similar cache for your map. Creating a map cache is recommended for optimum performance.

The Map caches section contains much detail about planning, creating, and updating map caches. There are several ways to create a cache, but the following steps are essential:

1. Right-click the service in ArcCatalog and click Service Properties.
2. Click the Caching tab and choose to draw the map "Using tiles from a cache that you will define below".
3. Click "Load tiling scheme from" and choose ArcGIS Online from the drop-down list.
4. If necessary, change the Cache directory.
5. Click Create Tiles. The caching tool appears with many values already filled in.
6. Uncheck any scales for which you do not want to create the cache. If your map covers a big area and will not be viewed at large (zoomed-in) scales, you should uncheck the large scales.
7. Set the update mode to Recreate All Tiles and click OK. The tool then creates the tiles.

Depending on how big your map is and the scales you've selected, it could take a long time to create all of the tiles. See Planning a map cache to learn about factors that influence cache creation time.

Once you've finished creating the cache, you're ready to use your map with ArcGIS Online services. See Developing with ArcGIS Server: An Overview to learn how you can develop JavaScript and Web ADF applications that overlay your maps with ArcGIS Online services.