It seems not improbable that the maps found in the MSS. of Ptolemy are really copies of, or derived from, original maps constructed by him or under his care. [AGATHODEMON, in Bloo. Div.] The geography of the Arabians is but imperfectly known. Their most eminent geographer Edrisi or Eldrisi, who lived about the middle of the 12th century, divided the world into seven climates irom the equator northward, and each climate was again divided into eleven equal parts, from the western coast of Africa to the eastern coast of Asia, the inconvenience of which arrangement is very obvious.
Towards the middle of the 17th century several astronomers under took to observe eclipses of the moon, with a view of correcting the errors in the longitude of places. These observations, however, were so discordant as to lead to no satisfactory result. Galileo, by the dis covery of the eclipses of the satellites of Jupiter, introduced a more certain method, which was rendered available by means of the simul taneous observations of Picard and Cassini at the observatories of Uraniburg and Paris.
Picard and Dc Labire were then immediately employed in correcting the map of France, and from this 1 eriod our maps have rapidly improved. The great perfection to which timekeepers have been brought, and the obvious application of these machines to the deter mination of the longitude, have greatly contributed to their accuracy. But notwithstanding the advanced state of our astronomical and geographical knowledge, and the science and skill displayed in our great national and other surveys, we may, with Dr. Blair, regard maps as works in progress—always unfinished, and still waiting the cor rections to be supplied by the science and enterprise of succeeding ages.
Having thus briefly sketched the progress of map-making, we pro ceed to give a general outline of the application and construction of maps.
On the Nature and Construction of being plane repre sentations of the surface of a sphere, may be obviously applied to various purposes; hence we not only have terrestrial maps to repre sent the surface of the earth, but celestial or astronomical maps to represent the sphere of the heavens ; and these general distinctions have again their subdivisions.
There are two kinds of terrestrial maps—geographic or land maps, and hydrographic or sea maps :-we shall confine our attention princi pally to the former ; the latter, which are usually called charts, having been already described. [CHART.]
Geographic maps, as already noticed, are those which represent the forums and dimensions of the several parts of the earth, with their relative situations and the positions of the citits, mountains, rivers, &c., comprised within their limits. They may comprehend the whole earth, or one of its larger divisions, or a single district, and are called maps of the world, general maps, or particular maps accordingly. If they give the nature of the ground, the roa ,s, buildings, &c., in detail, they become topographic maps, which, necessarily embracing a very small extent of country, are not usually referred to any spherical pro jection, but are represented as geometric planes, the objects in them occupying the positions severally assigned to them by the trigono metrical operations of the survey. The same distinction is made in charts of small bays and harbours. In either of these eases they are called plans.
When maps of the earth are made to illustrate any of the sciences, they are distinguished from geographic maps, properly so called, and bear their own peculiar names, as geological, or mineralogical, or botanical maps. A collection of such maps is called a physical atlas : such are the admirable atlases published by Berghaus, Johnston, and Petermann, in which the results of the investigations in geology, geography, hydrography, magnetism, meteorology, &e., are presented distinctly to the eye.
Of late years the leading governments of Europe have published maps showing, on a comparatively large scale, the results of elaborate trigonometrical surveys of the several countries : the maps of Austria and France are beautiful bxamples. In England, the results of the Ordnance Survey of a large portion of Great Britain and Ireland have been published in a series of admirable niape, at an extremely moderate price. The chief drawback is that, in the long intervals between the Publication of the different portions, material alterations are taking place with extraordinary rapidity. New railways are made; old roads are stepped up, and new Lines opened ; new towns spring up round railway stations, and villages become towns. Perhaps no mode of publication could be adopted to keep pace with these changes; and the plates are amended by laying down the new lines of railway when ever they are reprinted.