Strategies for creating map cache tiles

Map and image service caches can take a lot of server resources to create and store. If your cache is fairly small, you might be able to create tiles at all scale levels in an acceptable amount of time. If you cache has a broad extent or covers some very large scales, you may have to be more strategic about which tiles you create.

Creating a cache at small (zoomed out) scales is fairly easy, since it takes fewer tiles to cover the map at those scales. The small-scale tiles are also the ones most frequently visited, since people use them to get geographic context as they zoom in.

The large (zoomed in) scales are more expensive to cache, in terms of processing time and storage space. They are also less frequently visited than the small-scale tiles.

When you approach a large caching job, it's wise to build a full cache at the small scales and a partial cache at the large scales. The partial cache contains only the areas that you anticipate to be most visited. Uncached areas can be filled in with on-demand caching, or they can be displayed with a "Data not available" tile.

The diagram below shows how you could apply a strategic caching strategy to the prairie provinces of central Canada at large scales. Most of the population lives in the southern part of the provinces, as evidenced by the roads and towns there. You can precreate these tiles so that most users will immediately get the benefit of the cache.

The tiles for the rest of the map can be created on demand, since fewer users are likely to navigate there. The cost of creating, storing, and maintaining the cache for these vast uninhabited areas would outweigh the benefit of fast navigation for the first visitor.

You can run Manage Map Server Cache Tiles multiple times to spatially constrain tile creation for different subsets of scales.

Precreating tiles based on feature extents

How do you designate the portion of your map that will be precached? The simplest way is to precreate only the tiles that fall within the boundaries of a given feature class. The caching tools allow you to choose a feature class for this purpose. In the example above, you might provide a feature class containing one feature that covers all of southern Canada. Alternatively, you could draw the feature on the screen when you invoke the Manage Map Server Cache Tiles tool from ArcMap. In either case, providing a feature helps you avoid precreating tiles for vast uninhabited areas.

Caution:

On-demand caching creates all the tiles that are included in and around the map view, so the first time you visit an area with on-demand caching enabled, it may actually take longer to draw the map than if you were viewing the service dynamically. To improve performance, limit on-demand caching to areas that are not frequently viewed.