Setting visibility

When you look at Google maps or another web-mapping application, you can see that the map changes its style according to the zoom level. When you are looking at an entire continent, symbols are simple and there are a few features drawn on the map. As you get closer you can see more labels, major roads change their symbols, and minor roads appear.

This approach permits us to insert a large quantity of information on a web map while avoiding producing an almost unreadable crowd of labels and symbols. As an example, you can think of a cadastral map containing all USA parcels with a label showing owners. When you are looking at the entire country, it is impossible to show all this information without owning a several thousand inches wide display! A good approach would be to just show the country's boundaries and major roads and places on smaller scales and avoid showing parcels until you are not so close to see just a county.

The way to build such a map with SLD is by using...