DOCSLIB.ORG

6.4 MAP PROJECTIONS for LARGER-SCALE MAPPING* "Ohn

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text

Load more

6.4 MAP PROJECTIONS FOR LARGER-SCALE MAPPING* "ohn P. Snyder U.S. Geological Survey National Center, Stop 522 Reston, Virginia 22092 ABSTRACT After decaaes of using a single map projection, thc Polyconic, for its mp- i.ing program, the U.S. Geological Survey now uses several long-establjshcd ,-ojections for its published maps, both large and mal? scale. Tor naps cc 1:1,000,OCO-scale and larger, the most coimon projections are confowa:, such as the Transverse Mercator and Lambert Confornal Conic. projections for these scales should treat the Earth as an ellipsoid. In addition, the 'JSGS has conceived and designed some new projections, inc:udjng the Tpace Ob1 ique Vercator, the first nap projection designed to permit low-distortion {lapping of the Earth from satellite inagery, continucasly Collowing the graundtrack. The bSGS has programed nearly a1 1 yrti nent project ion equations for inverse and foniard calculations. These are used to plot naps or to transfom coordinates froill one projection to another. The CIS5 is also publishing its first comprehensive slap projxtion rcanual, describinq in detail and matheciatical ly all projections used by the agerlcy. The U.S. Geoloyical Scrvey wds created in 187c), and detailed large-scale napping 3f the country soon becane one of its primary objectives. Tt has relied heavily over the years 9n the foriner U.S. roast and Geodetic Survey (!JSC&GS, now the Yational Oceln Survey) &or guidance on nap projectiqns. Ati? the 1;te 1950's, only the Polyconic projection was used for the prirnary iJSGS napping product, i .e., large-scale quadrangle naps. The Polyconic projection was apparently 'nvented and certainly pronoted 5y f-erd-inand Rudolph Hassler, the first head of what was to hecoine known as the Coast and Geodetic Survey. In the 1959's, the USG5 quadrangle projection was changed to the Lanbert Co:iformal Conic and t.he Transve-w Mercator projec- tiocs, which had been adopted by the Coast and Geodetic Survey in the IQ3!7's for the State Plane Coordinate System. The developent of standardized zones bdsed upon the Universal Transverse Yereator and the polar Stereographic led to !JSGS use of these projections. Trl addition to these, the regii?ar Mercator, the Ob? ique Mercator, the Alhex Equal-Area hnic, and the .4zimith?l Equidistant have been used for other larger-scale nappinq by the IlSrS and other agencies. Although authors and organizations variously de <'inelarge- fYote: This paper is adaiited with sever31 ivodi'ications frmi one by the aiithor published it1 the ?roceedings of the 1381 ACSM Fall Technical Yeeting. and intermediate-scale mapping, for the purposes of this paper, the term "larger scale" will apply to scales larger than 1 to 2 million. When the space age added its impact to mapping, classical projections (Yercator, Lambert Conformal Conic, and Stereographic) were chosen fx the mapping of the Earth's Moon, three other planets, ana a nwber of other natural satellites. Some projections, especially the Space Oblique Mercator, originated within IlSGS to assist [napping from satellite imagery. TYPES OF PROJECTION Before describing the projections themselves, I 'd 1 ike to review Sriefly the different types. Equal-area or equivalent projections of the globe are used especially by geographers seeking to conpare land use, densities, and t.he like. On an equal-area projection, such as the Albers Equal-Area Con'c, a coin laid on one part of the map covers exactly the same area of the actual Earth as the same coin on any other part of the map. Shzpes, angles, and scale mst be distorted on most parts of such a map, but there are usually certain lines on an equal-area map as well as on other types of projections, along which there is no distortion Qfany kind. These so-called 'lst.dndard lines" nay be a merjdian, one or two parallels, lines which $re neither, or not a line but a point. More cononly used n larger-scale napping are conformal (orthmorphic) projections such as the Transverse Mercator and the Lambert Confornal Conic. The term nears that they are correct in shape, but, unlike the term "equal srea," :he conforma principle applies only to each infinitesimal elenent oc the nap. A.nqles at each point are correct, and consequently the local scale in every direction around any one point is constant, so the nap user can measure distance and direction between near points with a nininum oc difci- culty. Conformal maps mcy also be prepared by fitting together small pieces of other conformal nacs which have been enlarged or reduced; non-confornal projections rcqoire reshaping as well. When the region consists of more than a small element, distortioa in shape as well as area becomes apprecfable. This is especi&l!y serious with the most famous conformal projection -- the Mercator -- because cf its widespread use in classrooms, especiallj in the past. Recause tha-e is no angular distortion, all merid';;s intersect. parallels at right angles on a conformal pro<jection, just as the, 40 on the Earth. "Standard lines" may also be applied to a conformal ri,p to el irni- nate scale and area distortion along these lines and to t,iinimize distortion elsewhere. Sone nap projectims, such as the Azimuthal Equidistant, aye neither cqual- area nor confon,ial, but linear scale is correct along all lines radiating from the center, along mer'ldians, or following other special patterns. In additiotl, there are compromise projections, almost eqtirely restricted to srnall-scale mapping, which are used because they balance distortion in scale, area, and snape. 225 Projections are often classified by the type of surface onto which the Earth may be mapped. If a cylinder or cone that has been placed around a globe is unrolled, we have the concept gf cylindrical or conic projections, such as the Mercator or Lambert Confomal Conic, respectively. If the axis of the cone or cylinder coincides with the polar axis of the globe, the projection has equally spaced straight meridians, paral le1 on the cy1 indrical projections and converging on the conics. The paral le1s intersect the rwri- diaris at right dngles, being straight on the cylindricals and concentric circular arcs on the conics. The spacing of the parallels is seldorii projective. A plane laid tangent to the globe at the pole leads to polar azimlthal projec- tions, such as the polar Stereographic, with the parallels mapped as arcs of concentric circles and meridians as equally spaced rad'i of the circlt-1s. Scale reinains constant alony each parallel of latitude on a regular cylindrical, conic, or polar azimuthal projection, hut it changes one latitude to another. Directions of all points are correct as seen frog the center oc an azimuthal projection. If the cylinder or cone is secant instead of tangent to the glohe, the projec- tion conceptually has tw lines instead of one which are true to scale. Wrapping the cylinder about a meridian le,ids to tr3nsverse projections. Ry placiny a plane tangent to the Equator ixtead of a pole, equatorial aspects of azimuthal projections result. Tilting the cylinder, cone, or plane t,o reldte to another jioint on the Earth leads to an oblique projection, and the cieridians dnJ paral!els are 113 longer the straight lines or circular arcs they were in the norr:ial aspect. The lines of constant scale are correspond- inyly rotated. THE EAKTti h, IN ELLIPWID For i:iaps at scales si;ialler than 1:5,000,000, arld which cover regions larqer tha!i the Ilnited States , the distortions frwi i:iapping the spherical Earth' on flat p3per- are much greater than the slight additional corrections needed to coiqierisiite for the el 1 ipsoidal shape of the Farth. These corrections my then usually be ignored. The ellipsoid should be, and normdlly is, used for la;-ge-scale mapping of sm11 arms, or for loriq narroif strips. For such areas, the flattening of the round Earth (isual ly produces less distortion than the use of the sphere instead of the ellipsoid. A shift froin one ellipsoid to another has a negligible effect, ever1 on large- scale naps, upon the projected shdpes and positions of meridians and paral?cls. A yreater effect is the translat'on of latitude and longitude for all point,s 011 a liap, due to a change in datiii:i, that chan!,zs the position of +.he ellipsoid re1,qtive to the Larth. For this reason, the natation in tbe corsrier o+' !IS@, quadrangles stating "North nrerican Pat.uin 1927'' or "1933" is as important. ds the i.iardiiltltCrs of the vidp projection in defirii ng the basis of these naps. PR! NC IPAL PROJCCTIt!NS Polyconic Project icn About 18?0, Hdssler begdn to proi:iot.e the edsi ly const.ructed Polyconic ORIGINAL PAGE IS OF POOR QuAm c 0 .c Y 227 Gktiii4AL PAGE 13 OF POOR QUALITY projection as the basis of large-scale mapping. The USGS used this projec- tion for the earliest quadrangles, only changing in the 1959’s to other projections, although relabeling the map legend lagged considerably behind the change. The Polyconic is neither equal-area nor conformal. For 7-1/2- and 15-min. quadranyles, however, the distortion is negligible. Along the central meridian, it is free of distortion. Each parallel is also true to scale, but the other meridians are too long, and constantly change scale. The projection is not recoirunended for maps of considerable east-west extent cod, in fact, should not be seriously used for any new maps in view of other projections available. The parallels of latitude are circular arcs spaced at their true distances along the central meridian, but with radii equal to the length of the element of a cone tangent at the particular parallel.
Recommended publications
  • Nicolas-Auguste Tissot: a Link Between Cartography and Quasiconformal Theory

    Nicolas-Auguste Tissot: a Link Between Cartography and Quasiconformal Theory

    NICOLAS-AUGUSTE TISSOT: A LINK BETWEEN CARTOGRAPHY AND QUASICONFORMAL THEORY ATHANASE PAPADOPOULOS Abstract. Nicolas-Auguste Tissot (1824{1897) published a series of papers on cartography in which he introduced a tool which became known later on, among geographers, under the name of the Tissot indicatrix. This tool was broadly used during the twentieth century in the theory and in the practical aspects of the drawing of geographical maps. The Tissot indicatrix is a graph- ical representation of a field of ellipses on a map that describes its distortion. Tissot studied extensively, from a mathematical viewpoint, the distortion of mappings from the sphere onto the Euclidean plane that are used in drawing geographical maps, and more generally he developed a theory for the distor- sion of mappings between general surfaces. His ideas are at the heart of the work on quasiconformal mappings that was developed several decades after him by Gr¨otzsch, Lavrentieff, Ahlfors and Teichm¨uller.Gr¨otzsch mentions the work of Tissot and he uses the terminology related to his name (in particular, Gr¨otzsch uses the Tissot indicatrix). Teichm¨ullermentions the name of Tissot in a historical section in one of his fundamental papers where he claims that quasiconformal mappings were used by geographers, but without giving any hint about the nature of Tissot's work. The name of Tissot is also missing from all the historical surveys on quasiconformal mappings. In the present paper, we report on this work of Tissot. We shall also mention some related works on cartography, on the differential geometry of surfaces, and on the theory of quasiconformal mappings.
  • Mercator-15Dec2015.Pdf

    Mercator-15Dec2015.Pdf

    THE MERCATOR PROJECTIONS THE NORMAL AND TRANSVERSE MERCATOR PROJECTIONS ON THE SPHERE AND THE ELLIPSOID WITH FULL DERIVATIONS OF ALL FORMULAE PETER OSBORNE EDINBURGH 2013 This article describes the mathematics of the normal and transverse Mercator projections on the sphere and the ellipsoid with full deriva- tions of all formulae. The Transverse Mercator projection is the basis of many maps cov- ering individual countries, such as Australia and Great Britain, as well as the set of UTM projections covering the whole world (other than the polar regions). Such maps are invariably covered by a set of grid lines. It is important to appreciate the following two facts about the Transverse Mercator projection and the grids covering it: 1. Only one grid line runs true north–south. Thus in Britain only the grid line coincident with the central meridian at 2◦W is true: all other meridians deviate from grid lines. The UTM series is a set of 60 distinct Transverse Mercator projections each covering a width of 6◦in latitude: the grid lines run true north–south only on the central meridians at 3◦E, 9◦E, 15◦E, ... 2. The scale on the maps derived from Transverse Mercator pro- jections is not uniform: it is a function of position. For ex- ample the Landranger maps of the Ordnance Survey of Great Britain have a nominal scale of 1:50000: this value is only ex- act on two slightly curved lines almost parallel to the central meridian at 2◦W and distant approximately 180km east and west of it. The scale on the central meridian is constant but it is slightly less than the nominal value.
  • Map Projections--A Working Manual

    Map Projections--A Working Manual

    This is a reproduction of a library book that was digitized by Google as part of an ongoing effort to preserve the information in books and make it universally accessible. https://books.google.com 7 I- , t 7 < ?1 > I Map Projections — A Working Manual By JOHN P. SNYDER U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1395 _ i UNITED STATES GOVERNMENT PRINTING OFFIGE, WASHINGTON: 1987 no U.S. DEPARTMENT OF THE INTERIOR BRUCE BABBITT, Secretary U.S. GEOLOGICAL SURVEY Gordon P. Eaton, Director First printing 1987 Second printing 1989 Third printing 1994 Library of Congress Cataloging in Publication Data Snyder, John Parr, 1926— Map projections — a working manual. (U.S. Geological Survey professional paper ; 1395) Bibliography: p. Supt. of Docs. No.: I 19.16:1395 1. Map-projection — Handbooks, manuals, etc. I. Title. II. Series: Geological Survey professional paper : 1395. GA110.S577 1987 526.8 87-600250 For sale by the Superintendent of Documents, U.S. Government Printing Office Washington, DC 20402 PREFACE This publication is a major revision of USGS Bulletin 1532, which is titled Map Projections Used by the U.S. Geological Survey. Although several portions are essentially unchanged except for corrections and clarification, there is consider able revision in the early general discussion, and the scope of the book, originally limited to map projections used by the U.S. Geological Survey, now extends to include several other popular or useful projections. These and dozens of other projections are described with less detail in the forthcoming USGS publication An Album of Map Projections. As before, this study of map projections is intended to be useful to both the reader interested in the philosophy or history of the projections and the reader desiring the mathematics.
  • Arxiv:1811.01571V2 [Cs.CV] 24 Jan 2019 Many Traditional Cnns on 3D Data Simply Extend the 2D Convolutional Op- Erations to 3D, for Example, the Work of Wu Et Al

    Arxiv:1811.01571V2 [Cs.CV] 24 Jan 2019 Many Traditional Cnns on 3D Data Simply Extend the 2D Convolutional Op- Erations to 3D, for Example, the Work of Wu Et Al

    SPNet: Deep 3D Object Classification and Retrieval using Stereographic Projection Mohsen Yavartanoo1[0000−0002−0109−1202], Eu Young Kim1[0000−0003−0528−6557], and Kyoung Mu Lee1[0000−0001−7210−1036] Department of ECE, ASRI, Seoul National University, Seoul, Korea https://cv.snu.ac.kr/ fmyavartanoo, shreka116, [email protected] Abstract. We propose an efficient Stereographic Projection Neural Net- work (SPNet) for learning representations of 3D objects. We first trans- form a 3D input volume into a 2D planar image using stereographic projection. We then present a shallow 2D convolutional neural network (CNN) to estimate the object category followed by view ensemble, which combines the responses from multiple views of the object to further en- hance the predictions. Specifically, the proposed approach consists of four stages: (1) Stereographic projection of a 3D object, (2) view-specific fea- ture learning, (3) view selection and (4) view ensemble. The proposed ap- proach performs comparably to the state-of-the-art methods while having substantially lower GPU memory as well as network parameters. Despite its lightness, the experiments on 3D object classification and shape re- trievals demonstrate the high performance of the proposed method. Keywords: 3D object classification · 3D object retrieval · Stereographic Projection · Convolutional Neural Network · View Ensemble · View Se- lection. 1 Introduction In recent years, success of deep learning methods, in particular, convolutional neural network (CNN), has urged rapid development in various computer vision applications such as image classification, object detection, and super-resolution. Along with the drastic advances in 2D computer vision, understanding 3D shapes and environment have also attracted great attention.
  • Map Projections Paper 4 (Th.) UNIT : I ; TOPIC : 3 …Introduction

    Map Projections Paper 4 (Th.) UNIT : I ; TOPIC : 3 …Introduction

    FOR SEMESTER 3 GE Students , Geography Map Projections Paper 4 (Th.) UNIT : I ; TOPIC : 3 …Introduction Prepared and Compiled By Dr. Rajashree Dasgupta Assistant Professor Dept. of Geography Government Girls’ General Degree College 3/23/2020 1 Map Projections … The method by which we transform the earth’s spheroid (real world) to a flat surface (abstraction), either on paper or digitally Define the spatial relationship between locations on earth and their relative locations on a flat map Think about projecting a see- through globe onto a wall Dept. of Geography, GGGDC, 3/23/2020 Kolkata 2 Spatial Reference = Datum + Projection + Coordinate system Two basic locational systems: geometric or Cartesian (x, y, z) and geographic or gravitational (f, l, z) Mean sea level surface or geoid is approximated by an ellipsoid to define an earth datum which gives (f, l) and distance above geoid gives (z) 3/23/2020 Dept. of Geography, GGGDC, Kolkata 3 3/23/2020 Dept. of Geography, GGGDC, Kolkata 4 Classifications of Map Projections Criteria Parameter Classes/ Subclasses Extrinsic Datum Direct / Double/ Spherical Triple Surface Spheroidal Plane or Ist Order 2nd Order 3rd Order surface of I. Planar a. Tangent i. Normal projection II. Conical b. Secant ii. Transverse III. Cylindric c. Polysuperficial iii. Oblique al Method of Perspective Semi-perspective Non- Convention Projection perspective al Intrinsic Properties Azimuthal Equidistant Othomorphic Homologra phic Appearance Both parallels and meridians straight of parallels Parallels straight, meridians curve and Parallels curves, meridians straight meridians Both parallels and meridians curves Parallels concentric circles , meridians radiating st. lines Parallels concentric circles, meridians curves Geometric Rectangular Circular Elliptical Parabolic Shape 3/23/2020 Dept.
  • Uon Digital Repository Home

    Uon Digital Repository Home

    University of Nairobi School of Engineering Building a QGIS Helper Application to Overcome the Challenges of Cassini to UTM Coordinate System Conversions in Kenya BY Ajanga Dissent Ingati F56/81982/2015 A Project submitted in partial fulfillment for the Degree of Master of Science in Geographical Information Systems, in the Department of Geospatial & Space Technology of the University of Nairobi October 2017 I Declaration I, Ajanga Dissent Ingati, hereby declare that this project is my original work. To the best of my knowledge, the work presented here has not been presented for a degree in any other Institution of Higher Learning. ……………………………………. ……………………… .……..……… Name of student Signature Date This project has been submitted for examination with my approval as university supervisor. ……………………………………. ……………………… .……..……… Name of Supervisor Signature Date I Dedication I dedicate this work to my family for their support throughout the entire process of pursuing this degree and to the completion of the project. Your encouragement has been instrumental in ensuring the success of this project; may God truly bless you. II Acknowledgement I would like to show my heartfelt appreciation to all the people who saw me through the process of preparing this report. These thanks go to all those who provided technical support, talked through the issues I studied, read, wrote, gave comments, and also those who assisted in editing and proof reading of this project report before submission. I would like to thank Steve Firsake for his technical support through Python Programing. Special thanks also go to Dr.-Ing. Musyoka for his technical advice and support for the entire project.
  • The Influence of the Projected Coordinate System on Animal Home Range Estimation Area

    The Influence of the Projected Coordinate System on Animal Home Range Estimation Area

    University of South Florida Scholar Commons Graduate Theses and Dissertations Graduate School 11-4-2014 The nflueI nce of the Projected Coordinate System on Animal Home Range Estimation Area Michael Barr University of South Florida, [email protected] Follow this and additional works at: https://scholarcommons.usf.edu/etd Part of the Physical and Environmental Geography Commons Scholar Commons Citation Barr, Michael, "The nflueI nce of the Projected Coordinate System on Animal Home Range Estimation Area" (2014). Graduate Theses and Dissertations. https://scholarcommons.usf.edu/etd/5343 This Thesis is brought to you for free and open access by the Graduate School at Scholar Commons. It has been accepted for inclusion in Graduate Theses and Dissertations by an authorized administrator of Scholar Commons. For more information, please contact [email protected]. The Influence of the Projected Coordinate System on Animal Home Range Estimation Area by Michael R. Barr A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science School of Geosciences College of Arts and Sciences University of South Florida Major Professor: Joni Downs, Ph.D. Lori Collins, Ph.D. Elizabeth Walton, Ph.D. Date of Approval: November 4, 2014 Keywords: map distortion, GIS, characteristic hull polygon, map projections Copyright © 2014, Michael R. Barr ACKNOWLEDGEMENTS I would like to thank my committee members Dr. Walton and Dr. Collins for all of their valuable feedback and encouragement during this process. I would also like to thank the researchers whose data I have used in this thesis for making their work available. Special thanks to my advisor Dr.
  • A Critical Review of the Hypothesis of a Medieval Origin for Portolan Charts

    A Critical Review of the Hypothesis of a Medieval Origin for Portolan Charts

    A critical review of the hypothesis of a medieval origin for portolan charts i Roelof Nicolai A critical review of the hypothesis of a medieval origin for portolan charts Keywords: portolan, chart, medieval, geodesy, cartography, cartometric analysis, history, science ISBN/EAN: 978-90-76851-33-4 NUR-code: 930 Uitgeverij Educatieve Media, Houten. E-mail: [email protected] Vormgeving en drukwerkrealisatie: Atalanta, Houten Cover design: Sander Nicolai The cover shows part of the Carte Pisane, Bibliothèque nationale de France, Cartes et Plans, Ge B 1118. Copyright © by Roelof Nicolai All rights reserved. No part of the material protected by this copyright notice may be repro- duced or utilised in any form or by any means, electronic or mechanical, including photocopy- ing, recording or by information storage and retrieval system, without the prior permission of the author. ii A critical review of the hypothesis of a medieval origin for portolan charts Een kritische beschouwing van de hypothese van een middeleeuwse oorsprong voor portolaankaarten (met een samenvatting in het Nederlands) Proefschrift ter verkrijging van de graad van doctor aan de Universiteit Utrecht op gezag van de rector magnificus, prof.dr. G.J. van der Zwaan, ingevolge het besluit van het college voor promoties in het openbaar te verdedigen op maandag 3 maart 2014 des middags te 2.30 uur door Roelof Nicolai geboren op 20 november 1953 te Achtkarspelen iii Promotor: Prof. dr. J. P. Hogendijk Co-promotoren: Dr. S. A. Wepster Dr. P. C. J. van der Krogt iv He had bought a large map representing the sea, Without the least vestige of land: And the crew were much pleased when they found it to be A map they could all understand.
  • Bibliography of Map Projections

    Bibliography of Map Projections

    AVAILABILITY OF BOOKS AND MAPS OF THE U.S. GEOlOGICAL SURVEY Instructions on ordering publications of the U.S. Geological Survey, along with prices of the last offerings, are given in the cur­ rent-year issues of the monthly catalog "New Publications of the U.S. Geological Survey." Prices of available U.S. Geological Sur­ vey publications released prior to the current year are listed in the most recent annual "Price and Availability List" Publications that are listed in various U.S. Geological Survey catalogs (see back inside cover) but not listed in the most recent annual "Price and Availability List" are no longer available. Prices of reports released to the open files are given in the listing "U.S. Geological Survey Open-File Reports," updated month­ ly, which is for sale in microfiche from the U.S. Geological Survey, Books and Open-File Reports Section, Federal Center, Box 25425, Denver, CO 80225. Reports released through the NTIS may be obtained by writing to the National Technical Information Service, U.S. Department of Commerce, Springfield, VA 22161; please include NTIS report number with inquiry. Order U.S. Geological Survey publications by mail or over the counter from the offices given below. BY MAIL OVER THE COUNTER Books Books Professional Papers, Bulletins, Water-Supply Papers, Techniques of Water-Resources Investigations, Circulars, publications of general in­ Books of the U.S. Geological Survey are available over the terest (such as leaflets, pamphlets, booklets), single copies of Earthquakes counter at the following Geological Survey Public Inquiries Offices, all & Volcanoes, Preliminary Determination of Epicenters, and some mis­ of which are authorized agents of the Superintendent of Documents: cellaneous reports, including some of the foregoing series that have gone out of print at the Superintendent of Documents, are obtainable by mail from • WASHINGTON, D.C.--Main Interior Bldg., 2600 corridor, 18th and C Sts., NW.
  • Map Projections

    Map Projections

    Map Projections Chapter 4 Map Projections What is map projection? Why are map projections drawn? What are the different types of projections? Which projection is most suitably used for which area? In this chapter, we will seek the answers of such essential questions. MAP PROJECTION Map projection is the method of transferring the graticule of latitude and longitude on a plane surface. It can also be defined as the transformation of spherical network of parallels and meridians on a plane surface. As you know that, the earth on which we live in is not flat. It is geoid in shape like a sphere. A globe is the best model of the earth. Due to this property of the globe, the shape and sizes of the continents and oceans are accurately shown on it. It also shows the directions and distances very accurately. The globe is divided into various segments by the lines of latitude and longitude. The horizontal lines represent the parallels of latitude and the vertical lines represent the meridians of the longitude. The network of parallels and meridians is called graticule. This network facilitates drawing of maps. Drawing of the graticule on a flat surface is called projection. But a globe has many limitations. It is expensive. It can neither be carried everywhere easily nor can a minor detail be shown on it. Besides, on the globe the meridians are semi-circles and the parallels 35 are circles. When they are transferred on a plane surface, they become intersecting straight lines or curved lines. 2021-22 Practical Work in Geography NEED FOR MAP PROJECTION The need for a map projection mainly arises to have a detailed study of a 36 region, which is not possible to do from a globe.
  • Portraying Earth

    Portraying Earth

    A map says to you, 'Read me carefully, follow me closely, doubt me not.' It says, 'I am the Earth in the palm of your hand. Without me, you are alone and lost.’ Beryl Markham (West With the Night, 1946 ) • Map Projections • Families of Projections • Computer Cartography Students often have trouble with geographic names and terms. If you need/want to know how to pronounce something, try this link. Audio Pronunciation Guide The site doesn’t list everything but it does have the words with which you’re most likely to have trouble. • Methods for representing part of the surface of the earth on a flat surface • Systematic representations of all or part of the three-dimensional Earth’s surface in a two- dimensional model • Transform spherical surfaces into flat maps. • Affect how maps are used. The problem: Imagine a large transparent globe with drawings. You carefully cover the globe with a sheet of paper. You turn on a light bulb at the center of the globe and trace all of the things drawn on the globe onto the paper. You carefully remove the paper and flatten it on the table. How likely is it that the flattened image will be an exact copy of the globe? The different map projections are the different methods geographers have used attempting to transform an image of the spherical surface of the Earth into flat maps with as little distortion as possible. No matter which map projection method you use, it is impossible to show the curved earth on a flat surface without some distortion.
  • How to Determine Latitude and Longitude from Topographic Maps

    How to Determine Latitude and Longitude from Topographic Maps

    Oregon Department of Environmental Quality HOW TO DETERMINE LATITUDE AND LONGITUDE FROM TOPOGRAPHIC MAPS Latitude is the distance north or south of the equator. 2. For each location, construct a small rectangle around Longitude is the distance east or west of the prime the point with fine pencil lines connecting the nearest meridian (Greenwich, England). Latitude and longitude 2-1/2′ or 5′ graticules. Graticules are intersections of are measured in seconds, minutes, and degrees: latitude and longitude lines that are marked on the map edge, and appear as black crosses at four points in ″ ′ 60 (seconds) = 1 (minute) the interior of the map. 60′ (minutes) = 1° (degree) 3. Read and record the latitude and longitude for the To determine the latitude and longitude of your facility, southeast corner of the small quadrangle drawn in step you will need a topographic map from United States two. The latitude and longitude are printed at the edges Geological Survey (USGS). of the map. How to Obtain USGS Maps: 4. To determine the increment of latitude above the latitude line recorded in step 3: USGS maps used for determining latitude and longitude • Position the map so that you face its west edge; may be obtained from the USGS distribution center. These maps are available in both the 7.5 minute and l5 • Place the ruler in approximately a north-south minute series. For maps of the United States, including alignment, with the “0” on the latitude line recorded Alaska, Hawaii, American Samoa, Guam, Puerto Rico, in step 3 and the edge intersecting the point.