How to load a part of Image on Demand like GMap Does?

I have a big big image lets say 1000 MP (700MB), Like a Map of a particular area, What I want to do is load only the specific part if if zoom in to the image. This is important to make the app efficient to work in web.

I did it by storing the image by slicing it in various part and on demand load only that sliced image available.

The slices are done according to the zoom level.

But I don't want to do this way, Is there any efficient and proper way to do it, how any map does it ?