A method including (a) providing an amplification reagent including an array of sites, and a solution having different target nucleic acids; and (b) reacting the amplification reagent to produce amplification sites each having a clonal population of amplicons from a target nucleic acid from the solution. The reacting can include simultaneously transporting the nucleic acids to the sites at an average transport rate, and amplifying the nucleic acids that transport to the sites at an average amplification rate, wherein the average amplification rate exceeds the average transport rate. The reacting can include producing a first amplicon from a nucleic acid that transports to each of the sites, and producing subsequent amplicons from the nucleic acid or from the first amplicon, wherein the average rate at which the subsequent amplicons are generated exceeds the average rate at which the first amplicon is generated.