There are two principal differences between Google Maps and Earth that inform how things should ideally work under the hood. The first is the difference between fixed-view (often top-down) 2D & free-perspective 3D rendering. The second is between real-time and pre-rendered graphics. These two distinctions are fading away as the products improve and converge. But they highlight important differences, even today.
What both have in common is that they begin with traditional digital photography — lots of it — basically one giant high-resolution (or multi-resolution) picture of the Earth. How they differ is largely in how they render that data.
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