or Sea-Chart, an hydrographical map, or a projection of some part of the earth's superficies in plano, for the use of navigators. Charts differ very considerably from geographical or land-maps, which are of no use in navigation. Nor are sea-charts all of the same kind; some being what are called plane charts, others Mercator charts, and others globular charts.

Plane Chart is a representation of some part of the superficies of the terraqueous globe, in which the meridians are supposed parallel to each other, the parallels of latitude at equal distances, and consequently the degrees of latitude and longitude everywhere equal to each other.

Mercator's Chart is that where the meridians are straight lines, parallel to each other, and equidistant; the parallels also straight lines, and parallel to each other; but the distance between them increasing from the equinoctial towards either pole, in the ratio of the secant of the latitude to the radius.

Globular Chart, a meridional projection, in which the distance of the eye from the plane of the meridian, upon which the projection is made, is supposed to be equal to the sine of the angle 45°. This projection comes the nearest of all to the nature of the globe, because the meridians are placed at equal distances; the parallels also are nearly equidistant, and consequently the several parts of the earth have their proper proportion of magnitude, distance, and situation, nearly the same indeed as on the globe itself.

Hydrographic Charts, sheets of large paper on which several parts of the land and sea are described, with their respective coasts, harbours, sounds, flats, rocks, shelves, sands, and so forth, together with the longitude and latitude of each place, and the points of the compass.

Selenographic Charts, represent the spots, appearances, and maculae of the moon.

Topographic Charts, draughts of small parts of the earth, or of particular places.