INTRODUCTION This glossary has been prepared to provide the users and producers of cartographic products with definitions of technical terms used in mapping, charting, and geodesy. Mapping, charting, and geodesy encompasses practically all of the scientific disciplines and borrows copiously from their terminology. Therefore, it was recognized from the outset that, within the framework of time, manpower, and funds, this publication could not possibly include every word or term known or used within the Mapping, Charting, and Geodetic Community. The terms and definitions appearing in this publication were selected from existing glossaries and dictionaries, authoritative military and civilian sources, and technical publications and papers dealing with the various disciplines that make up the field of mapping, charting, and geodesy. For the most part, only those terms considered germane to some specific aspect of mapping, charting, and geodesy are included. In the peripheral or associated areas, such as photography, lithography, optics, mathematics, etc., only such basic terms were included as were considered necessary to establish a commonalty of language and, therefore, a means of better communication between these disciplines. To preclude the tendency toward overinclusion of terms from subject areas associated with mapping, charting, and geodesy, a decision was made to exclude certain types of words and terms. These included geographical, geomorphological, and map feature names; components of instruments and equipments; basic mathematical terms; units of lengths and measures; publication names; in-house terms and local colloquialisms; obsolete terms; terms which have no unique application to specific areas of mapping, charting, and geodesy or are of a generalized nature; ambiguous terms; terms that do not conform to acceptable Department of Defense or civil usage. Terms pertaining to map and chart specifications were also excluded as were terms dealing with marginal data. Drafting terms were omitted. Even though these terms are used widely in cartography, they are not unique to this discipline. This concept of term selection/exclusion has been extended into other related areas. In order that this glossary may serve the user with minimum effort on his part, the words/terms are arranged alphabetically, in the same manner in which they are spoken or appear in literature and followed immediately by a definition or a reference to the preferred synonym. Generally, the definitions are limited to a statement of the meaning of the term. Extended discussions are omitted except in instances where further amplification is considered essential. Definitions have been applied to the "preferred term" as determined by concensus from researching various sources. Other terms considered as synonyms are referenced to the preferred term. Disagreement on the selection of the preferred term may occur inasmuch as in-house or local usage usually influences one's choice of terminology. Words with multiple definitions have each definition numbered and, wherever applicable, identified with the appropriate discipline. At the end of some definitions, the user may be directed to see other terms appearing elsewhere in the glossary. Only those terms appear which have been defined. Synonyms are not included here although they can be found in their appropriate alphabetical order. This was done for a specific reason. The compilers of this glossary felt that there was nothing more exasperating than to be referred to an undefined term which further directed attention to the defined terms. The use of mathematical formulas, equations and expressions have been held to a minimum and, where possible, reduced to narrative form. Diagrams, sketches, or illustrations have not been used, although it was recognized that in many instances the use of a graphic presentation would be an aid in understanding the verbal definition. It is recognized that this glossary could not be all-inclusive. Therefore. if the user feels that the omission of certain terms detract from the utility of this glossary, he is encouraged to submit such terms together with their definitions for inclusion in future editions of this glossary. ABAC-A nomogram for obtaining the conversion angle to apply when plotting greatcircle bearings on a Mercator projection. A1 time—A particular atomic time scale, established by the U. S. Naval Observatory, with the origin on 1 January 1958, at zero hours UT2 and with the unit (second) equal to 9,192,631,770 cycles of Cesium at zero field. A-stations-1. (traverse) Subsidiary stations established between principal stations of a survey traverse, for convenience of measuring, to obtain the distance between principal stations. A-stations are so-called because in a given series, these stations are designated by the name of a principal station followed by the letters A, B, C, etc. in order of distance from the principal station. 2. (loran) The designation applied to the transmitting station of a pair, the signal of which always occurs less than half a repetition period after the next preceding signal and more than half a repetition period before the next succeeding signal of the other station of the pair, designated a B-station. aberration-1. (astronomy) The apparent angular displacement of the position of a celestial body in the direction of motion of the observer, caused by the combination of the velocity of the observer and the velocity of light. See also annual aberration; constant of aberration; differential aberration; diurnal aberration; planetary aberration; secular aberration; stellar aberration. 2. (optics) Failure of an optical system to bring all light rays received from a point object to a single image point or to a prescribed geometric position. See also astigmatism; circle of confusion; coma; curvature of field; distortion; lateral chromatic aberration; lens distortion; longitudinal chromatic aberration; spherical aberration. aberration of fixed stars-See secular aberration. A Abney level-A hand level with a vertical circle to which a bubble is attached. It can be used to measure vertical angles. abnormal magnetic variation-Any anomalous value whose cause is unknown, which occurs in some small local areas, containing sources which deflect the compass needle from the magnetic meridian. abscissas The distances parallel to the true (or orbitrarily assigned) east-west axis. More commonly called x-coordinates; also called total departures. absolute altimeter-An instrument which determines the height of an aircraft above the terrain. See also radar altimeter. absolute altitude-The height of an aircraft directly above the surface or terrain over which it is flying. See also radar altitude. absolute error-Absolute deviation, the value taken without regard to sign, from the corresponding true value. absolute orientation-The adjusting to proper scale, orientating the model datum parallel to sea level or other given vertical datum, and positioning the model with reference to the horizontal datum of a stereoscopic model or group of models. absolute parallax-See absolute stereoscopic parallax. absolute stereoscopic parallax-Considering a pair of aerial photographs of equal principal distance, the absolute stereoscopic parallax of a point is the algebraic difference of the distances of the two images from their respective photograph nadirs, measured in a horizontal plane and parallel to the air base. Generally shortened to parallax; also called x-parallax; linear parallax; horizontal parallax; stereoscopic parallax; absolute parallax. absolute term-A term (usually only one) in an equation, which has a known absolute numerical value and does not contain any unknown or variable elements. absolute unit-Any unit in a system that is based directly upon associated fundamental units of length, mass, and time. See also dynamic number. acceleration-1. The rate of change of velocity. 2. The act or process of accelerating, or the state of being accelerated. acceleration of gravity-The acceleration of a freely falling body due to the forces of attracting bodies. Its true value varies with latitude, altitude, local topographic and geological conditions and the mass of the parent body. accepted indicator-An airborne indicator which has been proven to be capable of accurate and reliable measurement. accidental error-An error that occurs without regard to any known physical law or pattern. Same as irregular error and random error. accommodation-1. The faculty of the human eye to adjust itself to give sharp images for different object distances. 2. (stereoscopy) The ability of the eyes to bring two images into super imposition for steroscopic viewing. 3. The limits or range within which a stereoplotting instrument is capable of operating. For example, the multiplex can adjust (or accommodate) for small tilts in the projectors ranging from about 10° about the x-axis to 20° about the y-axis. accumulated discrepancy-The sum of the separate discrepancies which occur in the various steps of making a survey or of the computation of a survey. accumulated divergence (leveling)-The algebraic sum of the divergences for the sections of a line of levels, from the beginning of the line to any section end at which it is desired to compute the total divergence. accumulative error-A constant error which is always plus or always minus. See also constant error; systematic error. accuracy-The degree of conformity with a standard, or the degree of perfection attained in a measurement. Accuracy relates to the quality of a result, and is distinguished from precision which relates to the quality of the operation by which the result is obtained. accuracy checking-The procurement of presumptive evidence of a map's compliance with specified accuracy standards. Accuracy checking generally indicates the relative (rather than the absolute) accuracy of map features. accuracy testing-The procurement of confirmed evidence, on a sampling basis, of a map's compliance with specified accuracy standards. Accuracy testing is designed to indicate both the relative and absolute accuracy of map features. accurate contour-A contour line, the accuracy of which lies within one-half of the basic vertical interval. Also called normal contour. acetate-A nonflammable plastic sheeting used as a base for photographic films or as a draft- | ing base for color separation manuscripts and overlays. achromatic lens-A lens which transmits light without separating it into component colors. achromatic telescope-A telescope having a mirror or an achromatic lens for its objective. aclinal Without dip; horizontal. aclinic-Without magnetic dip. aclinic line-See magnetic equator. across the grain-The direction opposite to that in which the paper fibers are aligned. Contrasted with grain direction. actinic light-Light which is capable of causing photo-chemical changes in a sensitized emul sion. active satellite-A satellite which transmits a signal, in contrast to a passive satellite. active tracking system-A system which requires addition of a transponder, or transmitter on board the vehicle to repeat, transmit, or retransmit information to the tracking equipment, such as SECOR. |