Glossary for Geospatial Science

projection or map projection:� �A device for representing all or part of a rounded surface on a flat sheet.� Since this cannot be done without distortion, the cartographer must choose the map characteristic [area, shape, scale, direction] which is to be shown accurately at the expense of others.� Map Projections Used by the U. S. Geological Survey, Geological Survey Bulletin 1532, Second Edition, U. S. Government Printing Office, Washington, D. C. , 1982, p. 5.

Every process that establishes or translates map projections offers the same standard selection list of projections.� The practical choice of map projections for ungeoreferenced project materials is normally determined by the kind of projection used by those project materials that are calibrated to a projection.� For example, if you have a scanned USGS topo map in the polyconic projection, you may decide to calibrate satellite images and vector overlays (or translate existing calibration) to the same projection.� (See also: ellipsoid.)