Map cache usage by clients

This topic contains three parts. The first section outlines how ArcGIS applications access and use the tiles in a map cache. The second part explains how these applications store the tiles for later use. The third section explains how to improve the display performance of tiles by adjusting the time a web browser reuses the tiles in its local cache. The final section provides some instructions for overlaying map caches in ArcGIS applications.

How applications access and use the cache

Once you define a tiling scheme for your map service, the service immediately begins trying to use the cache. Any ArcGIS application that can display a map service uses the cache, although how the tiles are retrieved and used varies between applications.

Web applications

When developing with the ArcGIS APIs for JavaScript, Flex, and Silverlight, you use a specific class to specify that you're connecting to a tiled (cached) map service. For example, with the JavaScript API, you use ArcGISTiledMapServiceLayer to connect to a cached service. When you use the cached service, tiles are retrieved from the cache directory by REST calls to the map service. The tile request takes the form http://<map service URL>/tile/<level>/<row>/<column>.

If you are viewing a single cached service in any web application and pan to an area where tiles do not exist, the application does not display a dynamic image; instead, you don't see anything. One way to ensure that you see a map when you pan to an uncached area is to enable on-demand caching.


If the map appears more slowly than expected, examine the URLs of the map images to verify that the application is retrieving tiles. One way to do this is to open the application in Mozilla Firefox and click Firefox > Web Developer > Web Console. When the console appears, click the Net button and zoom or pan your map.

  • If you see URLs like this, your application is successfully getting tiles from REST requests:

  • If you see some other URL format for your map images, your application is retrieving the tile in a less efficient way or the cache is not being used.


You add cached map services to ArcMap using the Add Data button, the same way you add any other map service. There are two ways you can view a cache in ArcMap:

  • Access the cache through a map service. To view a cache this way, browse to the GIS server and the map service used to create the cache. In this scenario, ArcMap makes an initial connection to the GIS server to determine if the service has a cache. ArcMap then retrieves tiles from the cache directory on the server's file system.
  • Access the cache as a raster dataset. To view a cache this way, browse to the directory containing the cache tiles and choose to add the dataset to ArcMap. The cache is represented with the same icon used to add all other rasters using the Add Data button. A cache accessed as a raster is for viewing only and cannot be queried. The advantage with this type of cache is that it is not tied to a map service and can be viewed when disconnected from the server, as long as you can still access the cache directory.

When a request is made for a tile at a scale that exactly matches a scale level in the cache, the map service returns the tile directly. Most often, requests do not exactly match the scale levels in the cache. In this situation, ArcMap generally requests the tile from the next closest scale level and resamples it to match the requested scale. This resampling is still much quicker than generating a tile dynamically; however, it does result in an image that looks different than the original tile. Map labels that have been cached may be difficult to read at certain scales in ArcMap due to this resampling. For best results, view the map at or near the scales from which the cache was created.

ArcGlobe and ArcGIS Explorer

ArcGlobe and ArcGIS Explorer can read 2D caches and drape them over the surface of the globe. You'll get the best performance if you build the cache with the ArcGIS Online/Google Maps/Bing Maps tiling scheme. If you cannot use one of these tiling schemes, your best performance will come from using globe services.

One scenario where you may want to add a map service to ArcGlobe is when you've created a 2D map cache and want to create an identical 3D globe cache from the 2D cache. In this scenario, you would only be concerned with generating the cache and would not be navigating the globe.

Improving the display performance of cached map services

When clients send requests to ArcGIS Server to display a map service, the response from the server is typically cached by the browser and reused for a certain period of time. This behavior helps ArcGIS Server achieve the best possible display performance for your map service. However, depending on how your map service and its associated data are used in applications, you may consider adjusting the length of time the browser will use a response in its cache. This can be achieved by adding a property named cacheControlMaxAge to the JavaScript Object Notation (JSON) of the service.

How the cacheControlMaxAge property is used

ArcGIS Server map service responses include an entity tag (ETag) and Cache-Control header. The ETag header value is a unique identifier of the response. The Cache-Control header has a max-age value that provides information to the browser regarding the maximum time period for which it can reuse a response from the browser's cache. This value is controlled by the cacheControlMaxAge property.

When a request is repeated and the maximum age of the cache has not expired, the browser will use the cached response without sending the request to the server. If the maximum age has expired, the browser must send the request to the server and set an IF-NONE-MATCH header with an associated ETag value corresponding to the response in its cache. ArcGIS Server evaluates the request and uses the ETag value to determine if the response has changed. If the response from the server is different from the copy on the browser, the server will send a completely new response to the browser. If the response is identical to the copy on the browser, the server alerts the browser to continue to use the response in its cache.

Defining the value of the cacheControlMaxAge property

As an ArcGIS Server administrator, you can define the cacheControlMaxAge property to specify how long a browser is allowed to use a cached response. By mitigating the need for ArcGIS Server to send a full response, you allow your browser caches to be more efficient, help optimize your applications, and save network bandwidth.

For cached map services that do not allow clients to cache tiles locally, the default is 0. This means the browser will always resend a request and ArcGIS Server will process the request and send a full response to the browser if the content has changed. This value works well for most applications.

For cached map services that allow clients to cache tiles locally, the default value is 86,400 seconds (1 day). This means that if a request is repeated within 1 day, the browser will use the response from its cache.

For cached map services where the map or data does not change frequently, it is recommended to increase the default to 30 days (259,2000 seconds) or longer to minimize network traffic.

To add the cacheControlMaxAge property to your service and specify its default value, do the following:

  1. In a web browser, open the ArcGIS Server Administrator Directory and log in with a user that has administrator privileges. The URL is formatted
  2. Click services and select the map service you want to modify from the Services list. If you don't see your service listed, it may be in a directory under the Root folder.
  3. On the Service - <service name> (<service type>) page, scroll to the bottom and click edit.
  4. In the Service Properties dialog box, locate the "properties" section of the service JSON.
  5. Add the cacheControlMaxAge property to the section and specify the value (in seconds) for the property, for example:
    "properties": {
      "cacheControlMaxAge": "2592000",
  6. Click Save Edits.
  7. On the Service - <service name> (<service type>) page, verify that the cacheControlMaxAge property and the value you specified for it appears in the Properties section.

Local caching of layers in ArcMap, ArcGIS Explorer, and ArcGlobe

ArcMap, ArcGIS Explorer, and ArcGlobe all maintain local caches of the tiles you have visited. When you zoom and pan back to these areas, the application uses the local cache and does not have to retrieve the tiles from the server again.

You can choose whether you want to save the local cache on disk for use in future sessions or use the local cache for the current session only.

You can also choose not to cache tiles locally. Although this causes you to lose the performance benefit of local caching, you can always be sure that you are getting the latest tile from the server.

It's possible that the server administrator has disabled local caching of the layer, which also means that you always get the most up-to-date tile. If this is the case, the other options for saving the cache locally are unavailable.

If the server administrator updates an area of the server cache that you have already viewed, you must clear your local cache to see the changes. ArcMap, ArcGIS Explorer, and ArcGlobe cannot detect if a cache has been updated. If you are a server administrator, you need to alert your users when updated data is available so that they know to clear their caches.

Overlaying caches

When designing map caches that will be overlaid with other map caches, there are some important cache design factors to consider depending on which application will be used to view the caches.

Overlaying map caches in web applications

Web applications such as the ones built with the ArcGIS APIs for JavaScript, Flex, and Silverlight require that you match coordinate system and tile size when overlaying caches. It's also a good practice to match as many scales as possible.

The easiest way to do this is to match tiling schemes for both caches, then only create tiles at the scales that make sense for each cache. This way, you can be sure that you've matched coordinate system and tile size and that the software recognizes that the two caches have scales in common.

Overlaying map caches in ArcMap

You can overlay any number of map caches in ArcMap. The caches do not need to have the same tiling schemes or projections; however, because of the resampling and reprojecting that ArcMap performs, using equivalent tiling schemes and projections may improve the performance and aesthetic quality of your map.

Forcing a dynamic draw

There are some occasions when you might want to force the service to ignore the cache and draw dynamically, even when tiles are available at some levels. For example, imagine you are developing a web application with the ArcGIS web APIs. You have a map that is cached from zoom levels 0 – 15, but should be drawn dynamically from levels 16 – 19. This might be the case if you want to show real time data at large scales, or if the map covers too broad of an area to be cached at large scales.

The solution for this scenario is to enable dynamic layers on the server and specify in your map requests at scales 16 – 19 that you want to use the dynamic layers. Otherwise, the service will return a map constructed from available tiles, which will be blank in areas where tiles don't exist.