In a bit more detail, google maps use a large element divcontaining several elements img. each of these elements imghas a size of 256 pixels and is located on a regular grid. from there, the Google Maps javascript program calculates which grid images should be loaded into each img tag and uses regular dom manipulation to place each img in the right place. Only the map tiles that will be visible inside the div are loaded. when you scroll side, the javascript library unloads the image and loads new ones as needed. Other elements, such as zoom controls, handles, and lines, are stacked or drawn on top of them as needed.