Download Map Projections - A Working Manual (U.S. Geological Survey by John P. Snyder PDF
By John P. Snyder
After many years of utilizing just one map projection, the Polyconic, for its mapping software, the U.S. Geological Survey (USGS) now makes use of a number of of the extra universal projections for its released maps. For better scale maps, together with topographic quadrangles and the kingdom Base Map sequence, conformal projections similar to the Transverse Mercator and the Lambert Conformal Conic are used. Equal-area and equidistant projections look within the nationwide Atlas. different projections, corresponding to the Miller Cylindrical and the Van der Grinten, are selected sometimes for comfort, occasionally applying current base maps ready through others. a few projections deal with the Earth in basic terms as a sphere, others as both ellipsoid or sphere. The USGS has additionally conceived and designed numerous new projections, together with the distance indirect Mercator, the 1st map projection designed to allow mapping of the Earth constantly from a satellite tv for pc with low distortion. The mapping of extraterrestrial our bodies has led to using typical projections in thoroughly new settings. a number of different projections that have now not been utilized by the USGS are usually of curiosity to the cartographic public. With elevated computerization, it is very important observe that oblong coordinates for these kinds of projections will be mathematically calculated with formulation which might have appeared too complex long ago, yet which now could be programmed repeatedly, particularly if aided by means of numerical examples. A dialogue of visual appeal, utilization, and historical past is given including either ahead and inverse equations for every projection concerned.
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Extra resources for Map Projections - A Working Manual (U.S. Geological Survey Professional Paper 1395)
Sample text
C) Sea-Floor Basalts One might have thought that all of the important igneous rock-types would have been discovered long ago. And yet, until recently, one major type remained hidden from view on the ocean floor, accessible only by dredging. The distinguishing features of these sea-floor basalts - their 32 Volcanic Rocks tholeiitic composition, their low contents of potassium and other large cations, their high K/Rb ratios, etc. - were established by ENGEL et al. (1965), and the first isotopic measurements were reported by T ATSUMOTO et al.
Helena these rocks are trachytes or phonolites; on Oahu they are tholeiites. On the other hand, in many instances trachytes, phonolites, and tholeiites do not have ratios Continental Volcanic Rocks 37 that are demonstrably higher than those of associated alkali basalts, although this may in part reflect insufficient precision of measurement. At present it does not appear that the 87Sr/86Sr ratios of normal tholeiitic basalts from oceanic islands differ significandy and consistendy from those of associated alkali basalts, although exceptions are known and both types from islands have higher ratios than the sea-floor basalts.
These granitic rocks collectively make up the large batholiths of the world, and many of the smaller stocks, laccoliths, dikes, and sills. They are by far the most abundant plutonic igneous rocks in the continental crust. If the scope of the definition were widened to encompass gneissic rocks of similar mineral composition, which may have had granites as parents, many of the rocks of the Precambrian Shield areas would also be included. Granitic rocks occurring in the major batholiths of the world, such as the Sierra Nevada Batholith of California, have been studied by many geologists, and several conflicting hypotheses regarding their origin have been proposed.