Dynamically Rendering in a Scrollable Area

What is the generic algorithm or process that is commonly used to dynamically render portions of a scrolling area?

For example, in Google Maps, when the user scrolls past the bounds of the currently rendered area, a grey checkerboard pattern is displ开发者_JAVA技巧ayed within the not-yet-rendered portions while the application loads and renders those areas.

I'm looking specifically for the approach, or the mathematics, related to filling a graphics area in chunks based on what has just come into view.

If possible, I'm looking for anything relevant to the GDI+ process of doing so.