- Industry: Earth science
- Number of terms: 93452
- Number of blossaries: 0
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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, ...
The image presented when the bubble in a spirit level is viewed through an optical system that shows the bubble split in half lengthwise, one of the halves being then reversed end for end and placed alongside the unreversed image. If the bubble is not exactly centered in the vial, the ends of the two halves will appear separated, longitudinally. When the bubble is centered, the ends of the image are aligned and one seems to be viewing one end of the entire bubble.
Industry:Earth science
An armchair-like valley having a steep, nearly vertical wall at the back (head), a concave floor meeting the back in a sharp break of slope, and a lip, at the front end (entrance), which may be of bedrock, glacial moraine or both.
Industry:Earth science
A nearly flat region of seismic activity (hypocenters) dipping, at continental margins or in continents, into the crust at an angle of about 45<sup>o</sup> and extending to depths of up to 700 km.
Industry:Earth science
The separation of map projections into sets according to criteria uniquely characterizing each set. Map projections are commonly classified either by the geometric quality preserved (i.e., left unchanged) by the transformation or by the kind of surface onto which the ellipsoid is mapped as an intermediate step in mapping onto the plane. The geometric qualities used are distances between points, angles, and areas within closed curves (or distances and areas scaled to the size of the map produced. ) A map projection keeping distances from a particular point or line unchanged except for scale is called an equidistant map projection; one keeping the angles between lines unchanged is called a conformal map projection; one keeping the azimuths from a particular point unchanged is called an azimuthal map projection; and one keeping areas within closed figures unchanged except for scale is called an equal area map projection. There are no generally accepted names for other sets. Map projections usually map the ellipsoid either directly onto the plane or first onto a sphere, cone, or cylinder and then from that surface onto the plane. If the map projection is from a cone or cylinder, the mapping onto the plane is done by the simple algebraic analog of unrolling the cone or cylinder. A spherical surface cannot be unrolled, but the algebraic transformations from ellipsoid to sphere and from sphere to plane are usually very much simpler than the single step process from ellipsoid to plane. A map projection using the cone as an intermediate surface is called a conical map projection; one using the cylinder is called a cylindrical map projection. There is no particular name for the set of map projections using the sphere as an intermediate surface. Except for the aposphere, which has been used as an inter-mediate surface for the transverse Mercator map projection, choice of intermediate surfaces has been pretty much limited to the sphere, the cone, and the cylinder. Map projections are also classified into two sets according as they are true projections (i.e., are equivalent to drawing straight lines from a given point, through the points on the ellipsoid, and onto the plane or intermediate surface) or are not. Those which are true projections are then further classified according to where the center of projection and the ellipsoid are placed with respect to the plane or intermediate surface. Many other schemes of classification exist but are comparatively little used. The best known are those of Maurer (1935) and Tobler (1962); there are more recent ones by Wray and Chovitz.
Industry:Earth science
The indication, on a hydrographic chart, of the chart or plan of next larger scale for some particular region.
Industry:Earth science
(1) One of the parts into which a vector may be divided and whose vectorial sum is the vector. For example, the vector representing the intensity of the Earth's magnetic field at a point can be considered the sum of the horizontal intensity and the vertical intensity, which are then the components. (2) One of the parts of a complete system.
Industry:Earth science
The level of intensity of competition among firms in a n industry, determined by an examination of five competitive forces.
Industry:Earth science
A circle, placed on the reticle of a transit or theodolite, with an angular radius of 15' 45" and centered on the intersection of the cross hairs. The Sun's radius on 1 July is 15'45" and is approximately the minimum for the year; there is a slight, noticeable overlap of the image from about September to April. In making observations, the image and the circle are taken concentrically to result in horizontal and vertical angles to the Sun's center.
Industry:Earth science
A diagram graduated according to the principles of the sun dial, designed to be placed on a plane-table or other flat and level surface, to determine the direction of astronomic north, relative to the direction of a shadow cast by a gnomon. It is much more accurate than a sun dial.
Industry:Earth science
