GTileOverlay on Google Map

Tile overlays are custom image/data that sit on top of an existing Google base map. The data/Image is cut into a pyramid of static tiles that correspond to each zoom level. Typically you would use some type of tool to cut the data into static tile images. In the figure below you see an example of a custom tile overlay showing AutoCAD map of university on top of a Google base map.

GTileOverlay is used when you want your data to overlay an existing Google Maps base map. In most cases you will want to use one of several tools available for creating the map tiles that will need to be displayed at each zoom level. GTileOverlay requires three abstract methods including getTileUrl(), isPng(), and getOpacity()

If you guys want more practical experience please play around this url http://npmap.np.edu.sg/