A monodisperse polystyrene (PS) film was spin-coated on a silicon wafer with native oxide layer and was in part scratched by a blade. Then, the surface modulus on a given area, in which PS and bared silicon were present, was two-dimensionally mapped as a function of temperature by scanning viscoelasticity microscopy. We visually present evidence that the PS surface started to soften up at a temperature much lower than the bulk glass transition temperature.