An experimental investigation is presented concerning the boiling of water at atmospheric pressure on a single copper surface in which the spatial distribution of active nucleation sites was investigated at different levels of heat flux and subcooling. The results obtained indicated that the active sites were located randomly on the heating surface, since the distribution of active sites followed the Poisson relationship. Changes in heat flux and sub-cooling did not affect the distribution of active nucleation sites although additional active sites formed among the sites which had already been activated when heat flux was increased. The frequency of vapor bubble emission and the bubble flux density have been studied as well. The results obtained showed that the heat flux had a great effect on the vapor bubble emission frequency although the influence of subcooling was of lesser significance. However, the bubble flux density was found to be non-uniformly distributed over the heating surface contrary to what had been expected.