This paper studies the impact of agglomeration and selection on firms' total factor productivity (TFP) distributions depending on their spatial location, specifically in science parks and large cities in Taiwan. The TFP distributions indicate a mean-shift and greater dispersion whenever firms benefit from agglomeration economies. However, selection due to competition may cause left truncation of the distribution. The empirical analysis shows that firms located in science parks have productivity that lags compared to those located in large cities and they benefit mainly from localization externalities.