Updating KML

The KML update feature is useful when you have already transmitted a large amount of data using a network link and subsequently want to change a relatively small amount of data in the previously fetched file. An alternative to using the <Update> element is to refresh the previously fetched file using a refresh based on time or change, as described in Chapter 6, Network Links. With time-based and view-based refreshes, the entire KML file (including all referenced models, textures, and images) is deleted from memory, refetched, and reloaded into memory. In contrast, with <Update>, only the specified elements are changed. The tradeoff, then, is that while an update requires a bit more framework to set up, greater efficiency can result for very large data sets.

There are three types of updates: