The maps are only used when resolving a 3 bird fix. As soon as you lock a fourth bird you can solve 3D directly rather than leveraging an onboard spheroid. Many

The maps are only used when resolving a 3 bird fix. As soon as you lock a fourth bird you can solve 3D directly rather than leveraging an onboard spheroid. Many receivers refer to a three bird fix as a 2D fix for that reason.