Overlaying map caches in the .NET Web ADF

When you create any cache that will be overlaid with another cache in the .NET Web ADF, the following items require attention:

Coordinate system of your map

You will achieve the fastest performance when your cached maps are in the same coordinate system. If you use different coordinate systems, only the cache of the primary map resource (see below) is used, and the server generates a dynamic image for all other services in the map, thereby forfeiting the performance benefit of those caches.

Scale levels

You will achieve the performance benefit of both caches only when the two caches have matching scale levels. In the case of a scale-level gap (when a scale level exists in one cache but not another), the overlaying image cannot be pulled from the cache and must be generated dynamically, thereby slowing performance. Image quality will also be degraded in this scenario, because the dynamic image must be resampled from one of the existing scale levels.

In the diagram below, Cache A does not exist at Scale 3; therefore, the .NET Web ADF will generate a dynamic image to overlay the image from Cache B at this scale.

Dynamic images are not created to match scales beyond the top or bottom scale of the cache. Therefore, for Cache A, a dynamic image will not be generated at Scale 5. Instead, Cache A will not be visible at Scale 5; only the cached image from Cache B will be displayed. Similarly, at Scale 1, only Cache A will be visible.

Image format

When choosing an image format for your caches that will be viewed in the .NET Web ADF, keep in mind the following points:

Setting the primary map resource in your Web application

In .NET Web applications containing more than one map service, the primary map resource determines which service will supply the coordinate system and zoom levels of the map. When you build a Web application in Manager, note the Use coordinate system and extent of drop-down list. The service you choose here becomes the primary map resource. If you use Visual Studio to build your Web applications, the primary map resource is a property of the Map control. Follow these guidelines for setting the primary map resource: