Demonstrates OpenLayer's facility for dealing with tiling artifacts.
When you render tiles with certain types of symbols, some map servers may render artifacts at tile edges that make symbology not look continuous. Look at the state abbreviations, open the layer switcher and change to the layer with a 15 pixel gutter to see how the symbology looks different (the server in this example doesn't render such artifacts, so the client-side gutter won't make things look nicer).