You should see your investment advisor about investing cash, but in this two part post we'll cover how you can best manage your investment in Explorer map cache. Under most circumstances cache and how it is managed are completely internal to the application. But knowing a little more about it will help you make the right decisions about managing your own cache, and in making decisions about how you connect to services. 

We'll begin by covering the implications of cache as it pertains to the default map, and other maps and layers you can access from the Content tab on the Explorer Resource Center.

Behind the scenes the default map and other maps are powered by ArcGIS Online, a large repository of online content and services that can be used in ArcGIS Explorer, ArcGIS Desktop, and ArcGIS Server. The ArcGIS Online services are powered by ArcGIS Server, and use ArcGIS Server's caching capabilities to streamline performance, and reduce client/server overhead. The ArcGIS Server 9.3 Help describes caching as follows:

Map caching is a very effective way to make your ArcGIS Server maps run faster. When you create a map cache, the server draws the entire map at several different scales, and stores copies of the map images. The server can then distribute these images whenever someone asks for a map. It's much quicker for ArcGIS Server to hand out a cached image than to draw the map each time someone requests it. Another benefit of caching is that the amount of detail in the image doesn't noticeably affect how quickly the server can distribute the copy.

The bottom line is that caching is a feature of ArcGIS Server that makes things better for you - the ArcGIS Explorer user.

When you first connect to a service you communicate with the ArcGIS Online's ArcGIS Servers. Cache is "handed out" to Explorer, and you'll see the Streaming... progress bar at the bottom of the map.

What's happening is that cache is being transferred from the ArcGIS Online servers to Explorer, where it's stored locally. This is somewhat similar to how bits and pieces of internet sites you visit are stored in browser cache to optimize performance when visiting the site again.

Once local, the next time you visit the same location Explorer doesn't even have to communicate with the server. It knows that it already has the cache it needs and simply uses it from local storage, resulting in best performance and minimizing client/server communications.

In an earlier post we blogged about how Explorer's default startup map and other layers you find on the Resource Center are regularly updated. To see these updates in areas that you've already visited you will have delete your local cache since Explorer knows you've already been there, and doesn't fetch new cache from the server.

But now that we said that, it's not entirely accurate. There were many changes in ArcGIS Online services in recent months that were automatically propagated to all Explorer users. That happened since we changed the ArcGIS Online server URL string to indicate a migration from the 9.2 version of ArcGIS Server to the 9.3 version. As a result of that change, new cache was pushed out automatically. But unless ESRI does something on the back end, some changes may be made to ArcGIS Online services that you'll need to refresh your cache to see.

To refresh your cache, just go to Tools > Options > Cache and choose Disk Cache. Check the option for All Caches and click Delete Caches.

It's a good idea to periodically refresh your cache, and good practice to make it part of your housekeeping activities.

In Part II, we'll cover how to have your cache refresh automatically when connecting to services.