Topographic map

“ A geologic map can not be constructed without an adequate base map. As in the west there were practically no adequate and systematic topographic surveys of the interior before the organization of state and federal geologic bureaus, it naturally fell to these organizations to construct base maps for their work. ”

“ These publications are illustrated with well-selected half-tones and carefully prepared black and white maps based on the accurate topographic maps issued by the Geological Survey.
The first need of the intelligent traveler is a map of the area he is about to traverse. Fortunately excellent maps of almost all the larger parks are for sale by the United States Geological Survey at nominal prices. Maps have been published of Yellowstone, Yosemite and Glacier national parks on a scale of 2 miles to the inch ”

“ It needs but little imagination to foretell that houses would be mere specks, roads, faint lines, and forests, masses of color, in other words, that it would be more instructive to consult the general map, on which all details are magnified to be clearly visible and topographic features brought out with great distinctness than to attempt to trace with unaided eye, from the image of objects at a distance of twenty-four miles, the course of streams or roads through forest or moor, or to judge of the relative elevations or modeling of the ground from the values of light and shade. ”

“ In the mountain regions of the West the geology is more complex, and the topography more intricate; but to a large extent these regions are uninhabited, and to a more limited extent uninhabitable. It would therefore not be wise to make a topographic or geologic survey of the country on an excessively elaborate plan. Over much of this area the sheets of the map will also be constructed on a scale of 1-250,000, but in special districts that scale will be increased to 1-125,000, and in the case of important mining districts charts will be constructed on a much larger scale. ”

“ The primary purpose of these topographic surveys is to provide the bases for geologic maps, yet these topographic maps, which cover 40 per cent of the area of the United States, are used in every type of civil engineering as well as by the public generally. The annual distribution by sale of half a million of these maps is an index of their value to the people. ”

“ The great value of the modern topographical map is becoming, however, universally acknowledged, and every highly civilized nation has either completed or has in preparation sectional topographical maps of its domain on such a scale as is warranted by its financial condition and its state of development. Thus there is now being accumulated a vast library of geographical and to some extent geological information, of which the student of geology must be prepared to make use. ”

“ The lines should preferably run across the long axis of an area, not parallel to it, and the predominating trend or general direction of the areas of one geologic formation on a map should decide the direction of the lines for all areas of that formation on the same map, even if the rule must be violated on some of the minor areas.
An effort should always be made to produce a pattern that is subordinate in strength to the main lines of the base map on which it is drawn. In black and white maps, as in colored maps, unlike patterns should be placed next to each other. ”

“ Map Projections are dealt with separately below. It will suffice therefore to point out that the ordinary needs of the cartographer can be met by conical projections, and, in the case of maps covering a wide area, by Lambert’s equal area projection. The indiscriminate use of Mercator’s projection, for maps of the world, is to be deprecated owing to the inordinate exaggeration of areas in high latitudes. In the case of topographical maps sheets bounded by meridians and parallels are to be commended. ”

“ A finished map border is used or omitted according to the kind of map prepared. Diagrammatic maps and maps on which no parallels and meridians appear do not need finished borders. On a map that shows complete areal geologic or other coloring, such as a map in a Survey geologic folio, the border lines tend to destroy the simple effect of the whole map. On a map that is not completely colored and on all very large maps borders are really necessary. ”

“ Commercial considerations are not to be overlooked; cheap and rapid methods of reproduction bring their temptations as well as their advantages to bear upon cartography. Their advantages are manifest; the map, whether as an adjunct to travel or as a graphic illustration of a great variety of subjects, has become a commodity of almost daily use. But in some countries, such as the United States, the standard of cartography generally is as low as that of the maps of the survey is high. ”

“ Ordnance maps of the United Kingdom are plotted, a meridian being chosen for a group of counties. It is also used for the 1-in., 1/2 in. and 1/4 in. Ordnance maps of England, the central meridian chosen being that which passes through a point in Delamere Forest in Cheshire. This projection should not as a rule be used for topographical maps, but is suitable for cadastral plans on account of the convenience of plotting the rectangular co-ordinates of the very numerous trigonometrical or traverse points required in the construction of such plans. ”

“ For a long time mountains were supposed to be the limitations of rivers, and old maps represent them always as flowing along the valleys without ever passing through the mountain-chains that divide them; but geology is fast correcting the errors of geography, and a map which represents merely the external features of a country, without reference to their structural relations, is no longer of any scientific value. ”

“ Great generalizations are not often completed at a single step, and it is enough that every effort at advance should have part of its movement in the right direction. What I wish to show is that topographic form was regarded in the days of our eastern surveys, even by our first master of American topography, as a completed product of extinct processes. Topography revealed structure, but it did not then reveal the long history that the structure has passed through. ”

“ When dealing with maps not drawn on an equal area projection we substitute quadrilaterals bounded by meridians and parallels, the areas for which are given in the “Smithsonian Geographical Tables” (1894) , in Professor H. Wagner’s tables in the geographical Jahrbuch, or similar works.
It is obvious that the area of a group of mountains projected on a horizontal plane, such as is presented by a map, must differ widely from the area of the superficies or physical surface of those mountains exposed to the air. Thus, a slope of 45° having a surface of 100 sq. m. ”

“ It is sometimes necessary to cut away the contour card; for, as has been already explained, a map is more or less generalized, and a contour is frequently carried across a ravine, instead of following it up, as it would do if the map were on a larger scale. Such generalizing is of course perfectly proper in a map, but, with the same scale, we expect more detail in a model. The modeler must have judgment enough and skill enough to read between the lines, and to undo the generalizing of the topographer and draughtsman, thus supplying the material omitted from the map. ”

“ Measurement of Distance.—The shortest distance between two places on the surface of a globe is represented by the arc of a great circle. If the two places are upon the same meridian or upon the equator the exact distance separating them is to be found by reference to a table giving the lengths of arcs of a meridian and of the equator. In all other cases recourse must be had to a map, a globe or mathematical formula. Measurements made on a topographical map yield the most satisfactory results. Even a general map may be trusted, as long as we keep within ten degrees of its centre. ”

“ The topographical survey of a country is defined by Sir A. Scott Waugh to imply ‘the measurement and delineation of the natural features of a country, and the works of man thereon, with the object of producing a complete and sufficiently accurate map. Being free from the trammels of boundaries of properties, the principal lines of operations must conform to the features of the country, and objects to be surveyed.’
The only safe basis for the topographical survey of a country is a system of accurate triangulation. ”

“ RUSKIN'S MAPS
Reading the map is as great a pleasure to some people as reading a story-book. You will see them pore over the atlas for an hour together, going on dream-journeys. It is a cheap way of globe-trotting, and gets rid of the discomforts; only one must have imagination to turn the wriggling hair-lines into vistas of river scenery, and the woolly-bear shading into forested crests and peaks against the sunset. It needs a good deal of imagination to get over the ugliness of most modern maps; but why should maps be ugly? ”

“ Anyone who attempts to draw a base map must, first of all, know how each feature or part of the map should be represented. Most of the conventional symbols for features shown on base maps are well established and should invariably be used; for instance, a line composed of alternate long and short dashes (not dashes and dots) represents a county boundary, and a line or two parallel lines across which short lines are drawn at regular intervals represents a railroad. ”

“ For instance, it is clear that in this case all meridian lengths are too small and all lengths along the parallels, except the equator, are too large. Thus although the areas are preserved the shapes are, especially away from the equator, much distorted.
The property of preserving areas is, however, a valuable one when the purpose of the map is to exhibit areas. If, for example, it is desired to give an idea of the area and distribution of the various states comprising the British Empire, this is a fairly good projection. ”

“ The complete atlas will consist of several thousand folios, each of which contains a topographical and a geological map of a small section of country, and will be named after some well-known town or natural feature within the limits of the district named. The topographical maps will show the reliefs, drainage, and cultures of the districts, indicated by the usual or definite conventional marks. The geological maps will show on distinct sheets the areal geology, or the areas occupied by the various rocks of the district; the economical geology, or the distribution of useful minerals ”

“ The map will indicate how near he came to the main outlines of the Mediterranean, of Northwest Europe, of Arabia, and of the Black Sea. Beyond these regions he could only depend upon the rough indications and guesses of untutored merchants. But it is worth while referring to his method of determining latitude, as it was followed up by most succeeding geographers. Between the equator and the most northerly point known to him, he divides up the earth into horizontal strips, called by him "climates," and determined by the average length of the longest day in each. ”

“ In this work the British hydrographic office may justly claim the credit of having contributed the chief share. Great Britain has likewise taken the lead in those deep-sea explorations which reveal to us the configuration of the sea-bottom, and enable us to construct charts of the ocean bed corresponding to the contoured maps of dry land yielded by topographical surveys. (E. G. R.)
Map Projections In the construction of maps, one has to consider how a portion of spherical surface, or a configuration traced on a sphere, can be represented on a plane. ”

“ Through the points thus obtained on the central meridian draw lines at right angles to the vertical line. Along these horizontal lines lay off the dimensions in the column headed X, Table 6 (pp. 39-47) of "Geographic tables and formulas" as required for each individual map—in the diagram every alternate degree. Draw vertical lines at these points and set off the distance Y in the same table in a similar manner, and the points so found will be the points of intersection of the respective meridians and parallels. Figures are given on the diagram for the thirty-fifth parallel only. ”

“ We read how the truths have appealed to his own consciousness. It stands where the relief map itself stands, as representing the delineator’s own mental image of such structure.
There are no lines drawn in this map that contradict or confuse the meaning; all is direct, truthful and clear in statement of fact. Each line has its own particular meaning. If represents direction. Applied to land surface, a vertical line means a perpendicular mountain or side wall of plateau, horizontal lines indicate level areas, and oblique lines a sloping surface. ”

“ Great care is necessary in the selection of stations that will be suitable both for the extension of triangulation and the purposes of closely overlooking topographical details. In order to obtain means for correctly orienting the photographic views when plotting the map from them, it is usual, whilst making the exposures, to observe two or three points in each view with the alt-azimuth attached to the camera, in order to ascertain the horizontal and vertical angles between them. ”

“ In the graphic representation of the surface they are far superior to the hachured map, and they have the further advantage of expressing the relative relief, which the hachured map fails to do, except in a very general way. They have also the advantage of showing actual shadows, exactly as they would be seen in a bird's-eye view of the district, instead of more or less conventional ones, and are, consequently, more easily comprehended by the layman, without becoming any less valuable to the skilled topographer. ”