Page images
PDF
EPUB
[graphic][ocr errors][ocr errors][ocr errors][ocr errors][ocr errors][ocr errors][ocr errors][ocr errors][ocr errors][ocr errors][ocr errors][ocr errors][ocr errors][ocr errors][subsumed][subsumed][subsumed][subsumed][ocr errors][subsumed][ocr errors][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][ocr errors][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][ocr errors][subsumed][subsumed][subsumed][subsumed][subsumed][ocr errors][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][merged small][subsumed][subsumed][subsumed][ocr errors][subsumed][subsumed][ocr errors][ocr errors][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][merged small][subsumed][subsumed][ocr errors][ocr errors][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][ocr errors][subsumed][subsumed][subsumed][ocr errors][subsumed][subsumed][subsumed][ocr errors][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][ocr errors][ocr errors][ocr errors][ocr errors][ocr errors][ocr errors][ocr errors][ocr errors][ocr errors][merged small]

winter season, he completes with great care the drafting of the maps, using the three colored inks selected as standard for this work-black for culture, blue for drainage, and brown for relief. Town and county maps are consulted, correspondence is entered into with postmasters and other local officials and railroad corporations, all compiled material is carefully scrutinized, and the final outlining of political boundaries and the lettering of names are completed.

These original drawings, as they are called, are at once copied by photography or photolithography, so that they may be available for immediate consultation by the public, pending their engraving on copper for final publication.

The cost of the surveys first made, on the scale of 4 miles to the inch, averaged $1.75 a square mile. Those made a few years later, on the scale of about 2 miles to the inch, averaged in cost $4 a square mile, while those made on the scale of approximately 1 mile to the inch, averaged in cost $10 a square mile. During the field season of 1884 a single party mapped over 11,000 square miles. A few years later the output of a single party, on the scale of 2 miles to the inch, was about 3,000 square miles in a season. To-day the more refined and detailed maps, on the scale of about 2 miles to the inch, with a contour interval of 100 feet, cost from $7 to $11 a square mile, according to the country, and a single party can rarely map over 600 to 1,000 square miles in a season. On the scale of 1 mile to the inch, a party now maps rarely more than 500 square miles in a season, and the cost of this work varies between $12 and $30 a square mile, according to the nature of the country.

The chief results accomplished by the topographic branch during the quarter-century are (1) a complete topographic map, published on 1,327 atlas sheets, of 929,850 square miles, or about 31 per cent of the area of the United States; and (2) the control by primary triangulation or traverse of approximately 587,000 additional square miles. In the completed work is included the running of more than 102,800 linear miles of spirit leveling, as a basis for the determination by less precise methods of the innumerable points locating contours. As a basis for the topographic mapping, the primary triangulation of the Coast and Geodetic Survey, of the Lake Survey and of the army engineers on the Mississippi and Missouri rivers, has been utilized where available, in addition to the primary triangulation and traverse by the Geological Survey.

The area mapped is as great as that of Austria, Belgium, Bulgaria, Denmark, France, Germany, Greece, Italy, the Netherlands, Portugal, Servia, Spain, Switzerland, and the United Kingdom of Great Britain. The work has necessarily cost a large sum. The appropriation in 1879 was $19,624; ten years later it was $218,200. The last appropriation (for 1903–4) aggregated over $300,000, which was augmented by allotments to this work from the appropriation for forest surveys and from State funds for cooperative purposes, bringing the total to nearly $500,000. The expenditure upon this work since its inception in 1879 has been $6,672,000.

Pl. V shows the areas that have been covered by the topographic surveys.

The results of the work of this division may be seen, also, by reference to the tables of atlas sheets and other maps in the Survey's list of publications.

Section of Triangulation and Computing. Since the inception of topographic work by the Geological Survey, primary triangulation and primary traverse have been executed on an extensive scale. At first topographers were assigned to the work of observing astronomic positions, measuring base lines, or extending primary triangulation. They acted, however, under the direction of the chiefs of the topographic sections, and frequently, in addition to their work as triangulators, were in charge of parties making topographic surveys. Gradually, as individuals evinced special aptitude for this work they were assigned to it exclusively.

As the work of the topographic branch increased it became evident that the part thereof which consisted of field triangulation and office computation needed systematizing, and therefore, in 1894, when the topographic branch was reorganized, it was separated into two divisions--one of triangulation and another of topography. For a few years the actual administration of the triangulation division remained in the hands of the chiefs of topographic sections; but in January, 1897, in order to secure uniformity in the office work connected with this division, a chief computer was appointed, under whom all office computations were conducted. In 1903, upon a further reorganization of the topographic branch, the division of triangulation was abolished and all the work of triangulation and computing was segregated in a section, the chief of which is in administrative charge of office computing. But, for convenience, the triangulation field work continues to be administered by the topographic section chiefs. During the last three years, however, the chief of the section of triangulation and computing has been in immediate charge of the field work of triangulation in the eastern section, under the direction of its chief.

For several years after the enactment of the law of 1896, authorizing and directing the running of careful spirit levels in connection with the topographic mapping, the office reduction and computation of results remained in the hands of the topographic chiefs. Gradually, as the work expanded, it became evident that for proper organization and supervision it should be made a separate section, and in 1901 the chief of the section of triangulation and computing was called upon to

[graphic]
[ocr errors]
[ocr errors]
[ocr errors]
[ocr errors]
[ocr errors]
[ocr errors]
[ocr errors]
[ocr errors]
[ocr errors]
[ocr errors]
[ocr errors]
[ocr errors]
[ocr errors]
[ocr errors]
[ocr errors]
[ocr errors]
[ocr errors]
[ocr errors]
[ocr errors]
[ocr errors]
[subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][ocr errors][ocr errors][ocr errors][ocr errors][ocr errors][ocr errors]
« ՆախորդըՇարունակել »