Abstract: A method for spatially tagging nucleic acids of a biological specimen, including steps of (a) providing a solid support comprising different nucleic acid probes that are randomly located on the solid support, wherein the different nucleic acid probes each includes a barcode sequence that differs from the barcode sequence of other randomly located probes on the solid support; (b) performing a nucleic acid detection reaction on the solid support to locate the barcode sequences on the solid support; (c) contacting a biological specimen with the solid support that has the randomly located probes; (d) hybridizing the randomly located probes to target nucleic acids from portions of the biological specimen; and (e) modifying the randomly located probes that are hybridized to the target nucleic acids, thereby producing modified probes that include the barcode sequences and a target specific modification, thereby spatially tagging the nucleic acids of the biological specimen.