map (cartography) app: dynamic multi-texures OGLES


I’m working on a OpenGL ES map application for the iPhone. The target is a development very simmilar to the well known Google Maps/Earth Application, but with my own map material. Especially the smooth dynamic loading of map-parts, scrolling and zooming I want to achieve like they did it.

I’m not an absolut beginner in OpenGL programming, altough I’m heavily struggeling with the conceptual design, especially according to the textures. At the moment I draw all the corner points of my map parts via VBOs to a triangle_strip via an indicesBO. My big problem is, how should I manage to load the missing map parts from the internet an add them to the actual texture(-image) and update the textcoords array, so that I achieve a good speed and though reduce the tranfers to the graphic cards ram? What is the best practice for such an approach? Could it even be better to abandon the VBOs and draw step by step?

thanks for your time