- Branche: 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 mirror reflecting light or other radiation mostly from the surface closer to the source. The word mirror as used by astronomers and other scientists almost always means a front-surface mirror. Front surface mirrors are sometimes made entirely of a substance which is a good reflector, e.g., silver. However, they are more usually made by evaporating a metallic such as silver or aluminum onto a suitably shaped material such as glass or quartz. To prevent the metal from tarnishing, silicon monoxide is usually evaporated onto the coated surface, forming a very thin layer of transparent silicon dioxide.
Industry:Earth science
A planimetric map prepared photogrammetrically for later inclusion of contour lines drawn in the field.
Industry:Earth science
A map projection mapping the rotational ellipsoid onto the plane according to the formula, for the sphere, x = k R (λ - λ <sub>o</sub>) and y = 4 k R (ln tan¼(π + mφ))/n , in which x and y are the rectangular Cartesian coordinates, in the plane, of that point which, on the sphere, has longitude λ and latitude φ λ<sub>o</sub> is the longitude of the central meridian on the map. R is the radius of the sphere and k is the scale factor. m and n are constants equal, in this instance, to 1.6 and 5, respectively. This map projection is neither conformal nor equal-area. Meridians and parallels are represented as straight lines, however. The projection was proposed by O.M. Miller in 1942 as a map projection giving a reasonable compromise between areal distortion and angular distortion. It was used by the United States Geological Survey for the National Atlas of the United States (1970). Values for m and n other than those given above have been used by some cartographers.
Industry:Earth science
For terms beginning with this word, see under the name of the specific method, e.g., for the method of equal-altitudes or the equal-altitude method, see equal altitude method.
Industry:Earth science
Any map projection mapping the meridians into lines not pointing approximately north and south at the equator, with respect to the neat lines of the map. Alternatively, any map projection mapping the equator into a line meeting the neat lines at an angle other than a right angle.
Industry:Earth science
The sum of the meridian distances of the ends of a surveyed line or course. In practice, assuming a closed traverse with the meridian of reference passing through the initial station, the double meridian-distance of the first course is equal to the difference of the meridian distances of the ends of that course; the double meridian-distance of each succeeding course is equal to the double meridian distance of the preceding course plus the difference of the meridian distances of the ends of the current course. If the double meridian-distance of each course is multiplied by the length of the arc between the parallels of latitude bounding that course, areas double those between the courses and the meridian are obtained; from these areas, the area of the tract being surveyed can be calculated. By a strictly analogous procedure, double parallel-distances can be calculated, using the latitudinal differences (in linear measure) of the successive courses instead of meridian differences and differences of meridian difference, and using a line running east and west as the parallel of reference.
Industry:Earth science
That point, on a map, whose coordinates are the medians of the coordinates of mapped points.
Industry:Earth science
A polyconic map projection obtained by substituting, for the central meridian, a great circle perpendicular to that meridian. This is done to provide an axis along which will lie the centers of the circular arcs representing lines of tangency of cones with the surface of the sphere. This is a complicated map-projection and the graticule is difficult to construct. However, it is useful for mapping, with comparatively little distortion, a narrow region of large extent eastward and westward.
Industry:Earth science
A map on which there are 1000 dots representing the distribution of some quantity, each dot representing 1/000 of the total amount and being placed on the map according to the evidence on the geographical occurrence of the quantity.
Industry:Earth science
(1) An angle exactly 1/60 of a degree or containing exactly 60 seconds. Sometimes called minute of arc. That term, however, is almost always unnecessary and should not be used unless confusion with the minute of time is likely. The symbol for minute (of arc) is ('). In astronomy, it is always placed immediately after the last integral digit of the number, i.e., above the decimal point if there is one; in other sciences, it is usually placed immediately after the last digit of the number. E.g., 35.'599 in astronomy and 35.599' in surveying. (2) An interval of time containing exactly 60 seconds of time or 1/60 of an hour. The minute is not a fundamental unit and therefore it has always been defined in terms of the second, the hour, or the day (which contains 1440 minutes.) The symbol for minute of time is (m). In astronomy, it is placed immediately after the last integral digit of the number, i.e., above the decimal point if there is one; in other sciences, it is placed immediately after the last digit of the number. E.g., 35.<sup>m</sup>599 in astronomy and 35.599 m in surveying.
Industry:Earth science
