The problem facing the designer of the new northern hemisphere map at Eureka's Fishermen's Terminal was no different from the one that ancient Egyptian mapmaker Ptolemy faced: How can you accurately transfer the curved surface of a sphere onto a flat surface? In 2,000 years the answer hasn't changed: You can't. No flat map can give a true scale representation of the world (or parts of the world) in terms of area, shape, position and distance.

Instead, map makers through the ages have created projections -- that is, methods to approximate all or part of the surface of the Earth on a flat surface. All projections are compromises. One will distort shapes for the sake of area accuracy. Another will sacrifice distances for correct bearings. Unlike a globe, a map is always an inaccurate model.

The three classic projections are conic, cylindrical and azimuthal (see diagram). All others -- there are literally hundreds -- are variants on these three basic methods. A conic projection imagines a light bulb at the center of the Earth shining through to a cone-shaped "hat" centered, typically, on the North Pole -- the cone is subsequently flattened out. A cylindrical projection has a cylinder of paper wrapped around the Earth as in the diagram. And an azimuthal projection imagines parallel rays of light shining through one hemisphere of the Earth onto a flat surface.

The Fisherman's Terminal map is a variant of the latter. Formally, it's an "azimuthal equidistant projection centered on the north pole," where the original azimuthal projection is adjusted so that lines of latitude are equally spaced. (A camera fisheye lens works the same way). For instance, latitude 45 north -- the circumferential concrete joint that crosses Oregon (see photo) -- is exactly midway between the north pole and the equator -- the map's boundary -- both on the map and in "real life." That's what makes it an "equidistant" map: Distances measured from the north pole scale correctly.

The creation of the map was a challenge in itself. According to local architect Philippe Lapotre of Lapotre and Cleek, full-sized stencil drawings were plotted for use as templates to mark the pattern on concrete. The contractor then used a router in the labor-intensive procedure of cutting a 1/4 inch groove along the land-sea boundaries before acid-etching the land (brown) and sea (blue).

The meter was originally defined as one ten-millionth of the distance from the pole to the equator. That's 6.4 meters on this map, giving a scale of about 1:1,560,000 -- but only if you're measuring along a line of longitude. Just don't use it to navigate across the Pacific!

Barry Evans' (barryevans9@yahoo.com) love affair with maps goes back to the Boy Scouts. The collection of his first 80 "Field Notes" columns is on sale at Eureka Books.