  We introduce regular charts as physical reference frames in spacetime, and we
show that general spacetimes can always be fully captured by regular charts.
Effective quantum field theories (QFTs) can be conveniently defined in regular
reference frames, and the definition is independent of specific background
metric and independent of specific regular reference frame. As a consequence,
coupling to classical gravity is possible in effective QFTs without getting
back-reaction effects. Moreover, we present an approach to effective QFTs
including quantum gravity.
