The idea behind tiling is to display a view by using several images rather than a single image. The static layers are represented by a grid of images of a fixed size. These fixed-size images are referred to as tiles. Dynamic layers are represented by a single image with a transparent background overlaying the view.

A static layer is not supposed to change during the application lifecycle and so can be generated once only. Typically, a static layer is the background of the view, such as a background map.

A dynamic layer contains objects, such as symbols, that can move and change their graphic representation.

The advantages of a tiled view are continuous panning and the capability of caching tiles. On the client side this avoids a roundtrip to the server and gives a better response time. On the server side it allows the server to receive the request, retrieve the image, and respond with the image without having to generate it. Not having to generate the image for the response is especially advantageous in complex applications.

Tile Size

The size of the tile determines the number of tiles needed to cover the view. The size must be carefully chosen, because it can have a considerable and potentially critical impact on performance. The larger the number of tiles needed because of their size relative to the size of the view to be covered, the more simultaneous requests to be addressed to the image servlet. There will also be more graphic objects to manage on the client side.

Cache Mechanisms

Since tiles in static layers are not subject to change, they can be cached on the client side to be reused directly without the need for a server roundtrip.

You can consider several possible strategies on the server side:

To manage the cache efficiently on the client and the server, the zoom levels must be fixed. If there is a free choice of what zoom level to apply, the probability of the client retrieving a cached tile is severely limited.