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ВЫБОР ПРОЕКЦИИ ТЕМАТИЧЕСКИХ КАРТ МОНГОЛИИ
Оюунцэцэг Даш
Горно-иженерный институт Монгольского университета науки и технологии, Бага Тойруу 34, Сухбаатарский район, г.Улаанбаатар, Монголия, зав. кафедрой геодезии и маркшейдерии, кандидат технических наук, доцент, тел. (976)11-452-485, e-mail: daoyunaa@must.edu.mn, daoyunaa@yahoo.com
Улзийсайхан Ганболдын
Горно-иженерный институт Монгольского университета науки и технологии, Бага Тойруу 34, Сухбаатарский район, г.Улаанбаатар, Монголия, преподаватель кафедры геодезии и маркшейдерии, тел. (976) 11-452-485, e-mail: ulziis.m@gmail.com
В статье рассмотрен вопрос о выборе конической проекции с двумя стандартными параллелями для тематических карт Монголии, определены искажения, а также построена сетка.
Ключевые слова: параметры проекции, стандартные параллели, искажения,
эллипсоид.
THE RATIONALITY OF MAP PROJECTION FOR THEMATIC MAPS IN MONGOLIA
Oyuntsetseg Dash
Mongolian University of Science and Technology, School of Mining Engineering, Baga Toiruu 34, Sukhbaatar district Ulaanbaatar, Mongolia, Head of Department of Geodesy and Mining Surveying, PhD, Professor, tel. (976) 11-452-485, e-mail: daoyunaa@must.edu.mn
Ulziisaikhan Ganbold
Mongolian University of Science and Technology, School of Mining Engineering, Baga Toiruu 34, Sukhbaatar district, Ulaanbaatar, Mongolia, Lecturer, Department of Geodesy and Mining Surveying, tel. (976) 11-452-485, e-mail: ulziis.m@gmail.com
For simplicity of description, most of this article describes the select of map projection with two standard parallels for thematic maps, as forth based on mathematic methods and determines the distortion value such as distance, area and direction.
Key words: parameter of projection, distortion, standard parallel, ellipsoid.
A thematic map is a type of map or chart especially designed to show a particular theme connected with a specific geographic area. Thematic maps are often described as small scale, typically soil, physical, social, political, cultural, economic, sociological, agricultural, road of Mongolian maps at a scale of 1:2500000.
A main thing of creating map is choosing map projection. It depends on geography of Mongolia and purpose. It normally used WGS-84 reference ellipsoid. Conformal normal conic projection with standard two parallels, it is a good choice thematic maps at a scale of 1:2500000 of Mongolia. As such it has straight line
meridians and circumference parallels with one circle center. The reason of choose map projection as follows are:
1. Mongolia is the world’s 19th largest country. It mostly lies between latitudes 41o and 52oN, and longitudes 87o and 120oE. So it necessitates a conical projection.
2. The developable surface may also be either tangent or secant to the sphere or ellipsoid. Tangent means the surface touches but does not slice through the globe; secant means the surface does slice through the globe. If latitude continued along between 61- 81, recommend to use conical projection with standard a parallel. And if latitude continued along between 101- 301, recommend to use conical projection with standard two parallels. About continued latitude of that Xw - Xe = 120o - 87o = 33o, because conical projection with standard two parallels is the best.
3. Main standard parallels are chosen by theory of Kavraisky V, such as follows:
9 i = 45o 9 2 = 49o
Mongolian thematic maps normally require a conformal projection, because it is used for education purposes. Hence, conformal conic projection with two standard parallels is more suitable for Mongolian thematic maps at a scale of 1:2500000. Parameters of that are: a = 0.731504204 N = 11726990.7m (on surface)
469,079628 cm (on map)
This projection shows distances and areas accurately. Result of estimation, distance (|u) and areal (p) distortions (on the standard parallels) as follows are:
^ = 0.99999 P = 1.00001
It is conformal conic projection, so distortion of direction is nothing. The correlation of distance and areal distortion of other parallels are shown in Fig. 1.
Figure 1. Distortion of areal and distance
The true grid of latitude and longitude represent is as follows: a map scale is 1:2500000, and a thematic map has two standard parallels, conformal normal conic projection. We used AutoCAD 2010 and calculated the projection grid by X and Y coordinates.
Figure 2. Grid lines of latitudes and longitudes
Conclusion
We took WGS-84 ellipsoid as the reference and chose standard parallel number 45o and 49o. The chosen conformal conic projection has no angle distortion (w=0) among the standard two parallels, the distance and areal distortion are adequate. Furthermore, these distortions of among the other parallels are adequate. Therefore, we recommend using this projection in industry and education. Besides, this projection is more suitable for production of thematic maps at a scale of 1:2500000.
© O. Dash, U. Ganbold, 2012
