- 行业: Earth science
- Number of terms: 93452
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Founded in 1941, the American Congress on Surveying and Mapping (ACSM) is an international association representing the interests of professionals in surveying, mapping and communicating spatial data relating to the Earth's surface. Today, ACSM's members include more than 7,000 surveyors, ...
A set of consecutive, binary digits, usually eight in number. One byte usually represents one character.
Industry:Earth science
The separation of maps into sets according to criteria uniquely characterizing each set. Maps are commonly classified according to (a) what geometric quality of the mapped region is preserved unchanged in the map; (b) the ratio (scale) between distances in the mapped region and lengths of corresponding lines in the map; (c) the region represented by the map; (d) the intended use of the map; (e) the type of information shown; or (f) some measure of the accuracy of the map. (a) Maps are classified as equidistant, conformal, azimuthal, or equal area according as they keep unchanged, except for scale, distances from a given point or line, angles between lines, azimuths from a given point, or areas within closed curves. An additional category is that of maps which introduce the smallest possible error (distortion) into the map under specified conditions (minimal distortion maps). (b) Maps are classified as large scale, medium or intermediate-scale, or small scale maps according as the average ratio between distances on the map and the corresponding distances on the ellipsoid is larger than some number used as criterion for the set, lies between that number and some smaller number selected as criterion, or is smaller than that second number. The criterion for large scale maps is usually 1/75 000 or larger; that for medium scale maps is usually larger than 1/1 000 000 - 1/500 000 is a common number. (c) Maps are classified as world maps, national maps, State maps, etc. , according to the size and location of the region represented. A world map (also called a global map) represents the entire Earth, a map of North America represents the continent of North America, etc. (d) There is no limit to the variety of uses to which a map may be put or for which it may be intended. However, some categories based on intended use are quite large: aeronautical charts and nautical charts take many different forms and the set contains many subsets; military maps, for tactical or strategic planning; route maps, for traveling by various means; and so on. (e) Classification according to the type of information shown is almost equivalent to classification according to intended use. In fact, it differs from that classification principally in having a general purpose category called topographic maps which show, symbolically, just about everything one would see if viewing the ground from a point well above it. Maps which are not topographic maps, i.e., which show only selected details or give, graphically, non topographic information are called thematic maps. Typical are maps showing the geologic structure of the crust (geologic maps), density of population (population density maps), the use to which land is being put (land use map), or the ownership of land (cadastral maps). (f) Classification of maps according to their accuracy is fairly standard for topographic maps, although the scheme varies in detail from country to country and from application to application. In the United States of America, a map of standard accuracy has been defined as one (a) meeting the National Map Accuracy Standards, (b) representing all features by symbols and treatments approved at the time of publication, (c) portraying cultural detail with reasonable completeness at the time of appraisal, and (c) having a contour interval representing all significant hypsometric detail (considering the scale of the map. ) Each actual map is then classified according to the extent to which it meets these standards, as follows: class 1 maps meet all four criteria; class 2 maps meet three of them, class 3 maps meet two of them, class 4 maps meet one or none of them, and class 5 maps may meet any or all of these criteria but have been superseded by maps of better quality.
Industry:Earth science
A ring with its perimeter graduated in angular measure and placed perpendicular to a vertical axis of rotation of an instrument, with the axis passing through its center. Horizontal circles of theodolites were formerly made of metal and were read through two microscopes placed 180<sup>o</sup> apart. In modern theodolites, the horizontal circle is made of glass and is read through a single microscope which, by a prismatic train, lets the observer see the two opposite sides of the circle simultaneously.
Industry:Earth science
A chart designed primarily for directing and conducting searches and rescues.
Industry:Earth science
(1) The process of preparing a separate drawing, engraving, or negative for each color required in printing a map. For instance, one drawing would be prepared showing only streams, lakes, and so on; another would show only contour lines; still another would show only man made features. (2) A photographic process or electronic scanning procedure using color-filters to separate multicolored copy into separate images in each of the three primary colors.
Industry:Earth science
One or more optical elements treated as a unit, for example, a cemented doublet or a Nicol prism.
Industry:Earth science
A coordinate system consisting of three (or two) straight lines (called the axes) intersecting at a common point and perpendicular to each other; the coordinates of a point are the distances to the point from the three planes defined by the three pairs of axes (or from the two axes). This is equivalent to specifying a coordinate system which is rectangular and Cartesian.
Industry:Earth science
(1) An optical instrument providing for the use of both eyes simultaneously. (2) A pair of eyepieces or telescopes placed side by side so that both eyes can observe simultaneously. The term pair of binoculars is often used instead. Note that observing through a binocular does not necessarily give binocular vision. Microscopes are often provided with binocular eyepieces but only a single objective. Both eyes therefore look at the object from exactly the same viewpoint.
Industry:Earth science
A description of the boundary of a piece of land in terms of adjoining land or waters. For example, bounded on the north by the Potomac River, on the west by Turkey Run Park, on the south by the land of Joseph Taylor, and on the east by Turkey Run.
Industry:Earth science
