The readme contains a lot of the implementation details: "We use three different tables with different levels of detail: planes_mercator contains 100% of the data, planes_mercator_sample10 contains 10% of the data, and planes_mercator_sample100 contains 1% of the data. The loading starts with a 1% sample to provide instant response even while rendering the whole world. After loading the first level of detail, it continues to the next level of 10%, and then it continues with 100% of the data. This gives a nice effect of progressive loading."