Wide field imaging can be subdivided in terms of wavelengths, the kinds of emission sought, data types, richness of field, detector types, astronomical objects to be investigated, and probably other ways. These are surveyed with special reference to the talks given in Potsdam, ending with a handful of issues about which disagreement, or at least discussion, persists.

Wide field can mean many things. V. Lipovetsky defined it as imaging with 107–8 elements or pixels per field. There are other possibilities. For neutrinos, gravitational radiation, cosmic rays, and (some kinds of) gamma rays, the whole sky is a single (very wide) field. At the other extreme, the HST ‘wide field’ camera covers about 2′ and needs nearly 4 × 107 exposures to survey the sky. In between, the POSS and ESO/SERC Schmidt plates see 6° at a gulp, interestingly similar to the roughly 6° sharp central cone of human vision (you can test this by holding a book at a measured distance from your face and counting how many times your eyes jump in reading a line).