These methods enable map makers to control the distortion that. Methodology and assumptions for the population projections. The influence of map projections on peoples globalscale. Conformal projections retain correct angular relations in transfer from globe to map. Page 79 discuss map scale and the basics of coordinate systems. In conformal map projections also known as orthomorphic or autogonal projection local angles are preserved. Maps were devised because they are much easier to use, store, and transport than globes, and they facilitated the development of much larger scaled representations than was the case with a globe. In addition, a number of map projections are based on polyhedra.
Scale same in any direction around a point, but scale changes from point to point. Since you can filter by projection type in the selection by thumbnail, id like to offer a brief introduction to the different types available i will confine myself mostly to optical differences, i am not going to explain how they are constructed mathematically or why they are called. However, map projections have distortions which depend largely on the size of the area being mapped. For larger scale maps, including topographic quadrangles and the state base map series, conformal projections such as the transverse mercator and the lambert conformal conic are used. Understanding map projections paperback july 1, 2001 by melita kennedy author, steve kopp author 3. The importance of map projections by sarah lyle on prezi. A gis is a system for the display, analysis, storage and retrieval of information about places on the earth. Armed forces military maps show the earth drawn to scale as you would see it from above the military uses the universal transverse mercator utm and the universal polar stereographic ups grid system. This is a digital copy of a book that was preserved for. An introduction to the study of map projections nature. Apr 25, 2017 however, map projections have distortions which depend largely on the size of the area being mapped. Introduction in australia, largescale topographic mapping and survey coordination is based on rectangular grids overlaying conformal map projections.
Methodology and assumptions for the population projections of. Map projections with a equalarea distortion property on the other hand, represent areas correctly, but as the region becomes larger, it shows considerable distortions of angles and consequently shapes figure below. Direction or azimuthal projections maintain some of the greatcircle arcs, giving the directions or azimuths of all points on the map correctly with respect to the centre. In all the map projections we will be dealing with, the datum surface is a 3dimensional surface, either a sphere or ellipsoid, representing the earth. Azimuthal, or planar projections can have different perspective points. Understanding map projections landing page for kartoweb. See all 2 formats and editions hide other formats and editions. Use the printable worksheet to pinpoint study points to look. Projections by presentation of a metric property would include equidistant, conformal, gnomonic, equal area, and compromise projections. What is the importance of map projection in geographic. The term map projection can be thought of literally as a projection. Another serious limitation of this projection is that only a portion of the earths. Some projections have equalarea properties, while others provide for conformal delineations in which, for small areas, the shape is.
A datum provides a frame of reference for measuring locations on the surface of the earth. Map projections coach grigg ap human geography golf. Antiti map projections tn 6 a map is a representation of all or part of the earth drawn on a flat surface at a specific scale. Developing a cognitive map requires spatial knowledge, which humans. Only the tm and utm projections are considered in this paper. This orthographic projection distorts distance, shape, and the size of areas.
This is a summary of map projections that have articles of their own on wikipedia or that are otherwise notable. If it is your first time using the course, start with part 1. After decades of using only one map projection, the polyconic, for its mapping program, the u. Map makers attempt to transfer the eartha round, spherical globeto flat paper. In cartography, a map projection is a way to flatten a globes surface into a plane in order to make a map. The stereographic map projection is most useful for maps of polar regions for navigation purposes or large continentsized areas of similar extent in all directions. A gcs is often incorrectly called a datum, but a datum is only one part of a gcs.
And now we can project and unproject massive quantities of coordinates, transforming them backward and forward from latitude and longitude assuming this or that earth model to overlay precisely with data that are stored in some other coordinate space. Creating map projections used to be a very hard thing to do. Mercator projection wraps a cylinder around the earth. The illustrations below show some of the common map projections used today. This data uses a sinusoidal projection, which is an example of an equalarea projection. Therefore we must use a projection and none are really true to the actual spherical location. The central focus of this book is on the theory of map projections. Shine a light from the center of the earth, trace the image that is projected onto the paper, and then take the paper o. Since the earth is roughly the shape of an oblate spheroid, map projections are necessary for creating maps of the earth or parts of the earth that are represented on a plane such as a piece of paper or a computer screen.
A map projection systematically projects locations from the surface of a spheroid to representative positions on a flat surface using mathematical algorithms. Map projections tn 6 a map is a representation of all or part of the earth drawn on a flat surface at a specific scale. However, map projection refers specifically to a cartographic projection. Pseudocylindrical projection outlines tend to be barrelshaped rather than rectangular. All map projections must distort size, shape, distance, or direction. Invented in the 16th century, the projection is that of the sphere on a cylinder tangent to the equator. If we were to place a light bulb inside a translucent globe and project the image onto a wallwed have a map projection. Jan 22, 2011 the usgs has posted a scanned file of john p. Map projections cartographers have to deal with the problem of making maps of a spherical earth onto a flat surface leads to distortions shape can be distorted distance between two points can increase or decrease relative size may be altered, areas can appear much larger than. Only a globe preserves the map qualities of area, shape, direction, and distance.
Purchase coordinate systems and map projections 2nd edition. The mcd12q1 land cover dataset for 2012, in its native sinusoidal map projection. Models of map projections there are two models for creating different map projections. Decide which map projection to use for your gis project. Click on skip the slideshow to start your elearning session immediately. The subject of map projections, either generally or specifically, has been dis. The gnomonic projection s point is at the center of the globe. Summary 2 we can project onto a plane, a cylinder or a cone. Steerss useful little book on map projections, the third edition of which has recently been issued, is written for those students of geography who have only the most elementary knowledge of. Another way of classifying map projections is to consider the earth as a transparent sphere. There is no limit to the number of possible map projections 1 projections are a subject of several pure mathematical fields, including differential geometry, projective geometry, and manifolds.
All projections of a sphere on a plane necessarily distort the surface in some way and to some extent. Maps and map reading are essential skills that all of the armed forces need. This course explores categories of map projections and their properties. Feb 21, 2011 conformal projections retain correct angular relations in transfer from globe to map. Since the mass of the earth is not uniform at all points, and the direction of gravity changes, the. Map projections a map projection is a method of representing a portion of the earths round surface on a flat surface. The beginning of the book contains substantial introductory information about map projection families and distortions. Similarly constant local scale is maintained in every direction around a point. A map projection s aspect is its orientation on the page or display screen. What is a map projection map projection definition.
The stereographic map projection is conformal but not. Some truedirection projections are also conformal, or equalarea, or equidistant. Equalarea and equidistant projections appear in the national atlas. The stereographic map projection is another ancient projection, dating back to the second century b. Some common examples are cones, cylinders, and planes. Some projections treat the earth only as a sphere, others as either ellipsoid or sphere.
The first twodimensional projection shows the earths surface as viewed from space figure 2a2. However, they do resemble cylindrical projections, with straight and parallel latitude lines, and can have equally spaced meridians, but meridians are curves, not straight lines. Learn which projections are best for different types of gis maps and how to choose a projection for a given mapping project. A map projection is a method for taking the curved surface of the earth and displaying it on something flat, like a computer screen or a piece of paper.
Introduction to map design introduction this document is intended to help people without formal training in map design learn to produce maps for publication or electronic display using arcview, a desktop geographic information system gis. Basics of map projections esri training web course. A gcs includes an angular unit of measure, a prime meridian, and a datum based on a. Snyderand harry steward editor of revisions 1st edition. A sound knowledge of map projections and grids requires an understanding of the mathematical nature of projections and the size and shape of the earth, since in our context. When the central axis of the developable surface is oriented eastwest, the projection s aspect is. Map projections can be created mechanically or mathematically.
Because maps are flat, some of the simplest projections are made onto geometric shapes that can be flattened without stretching their surfaces. They are used to classify the majority of projections, including some that are not analytically geometrically constructed. The shape of the earth and the geodetic datum concept are covered on pages 46. Geological survey usgs now uses several of the more common projections for its published maps. Map projection definition of map projection by the free. Coordinate systems and map projections 2nd edition. The geoid is defined as the surface of the earths gravity field, which is approximately the same as mean sea level. Cylindrical wrap a piece of paper around the earth to form a cylinder that touches the equater all the way around the earth. Map projections are introduced on pages 1012, and pages. Although the earth is best represented by a spheroid, the earth is sometimes treated as a sphere. However, instead of projecting a light, cartographers use mathematical formulas to.
Map makers have devised methods for taking points on the curved surface of the earth and projecting them onto a flat surface. The circle gives the impression that worcester is approximately the same distance from boston as new hampshire, and that the state is nearly five times longer, east to west, as it is northtosouth. A great variety of map projections has been devised to provide for the various properties that may be desired in maps. The post1973 editions of the alaska map e more nearly approximate an equidistant conic map projection. Some truedirection projections are also conformal, equal area, or equidistant. True earth to globe lengths scaled by the representative fraction e. A tutorial on map projections and geographic coordinate systems. The map of massachusetts in unprojected decimal degrees of longitude and latitude note the proportion of the lines and the circle. Because there is no limit to the number of possible map projections, there can be no comprehensive list.
Bibliography of map projections editors of first edition. A map projection is a geometric function that transforms the earths curved, ellipsoidal surface onto a flat, 2dimensional plane. Since you can filter by projection type in the selection by thumbnail, id like to offer a brief introduction to the different types available. Map projections are based on developable surfaces, and the three traditional families consist of cylinders, cones, and planes. Scale distortions on maps are shown on the map by an ellipse of distortion or using scale factor which is the ratio of the scale at a given point to the true scale. It is perpendicular to the direction of gravity pull. Since the mass of the earth is not uniform at all points, and the direction of gravity changes, the shape of the geoid is irregular. Aspect individual azimuthal map projections are divided into three aspects. This requires a systematic transformation of the latitudes and longitudes of locations from the surface of the globe into locations on a plane. Name date comparing map projections to the globe analyze the maps on the map projections handout and a globe to complete the charts below. The study of map projections is the characterization of these distortions.
Large areas tend to look more like they do on the globe than is true for. The surface of a sphere cannot be represented as a flat map. If north or south is straight up, the aspect is said to be equatorial. A map projection is the mathematical transformation of coordinates on a. All cylindrical projections fill a rectangular plane. Mathematical cartography also takes in map scales and their variation, the. Geological survey bulletin 1856, 1997 also two online editions installed at ohio state university, 1994, 1996 under supervision of eric john miller and duane f. In effect, a projection is a systematic method of drawing the earths meridians and parallels on a flat surface.
Maps were devised because they are much easier to use, store, and transport than globes, and they facilitated the development of much larger. A scale tells you the ratio of a distance on the map to the actual distance in real life. Map projection concerns the science of mathematical cartography, the techniques by which the earths dimensions, shape and features are translated in map form, be that twodimensional paper or two or three dimensional electronic representations. Introduction a map is a representation of all or part of the earth drawn on a flat surface at a specific scale. The opposite side of the globe from the point of contact is used for a stereographic projection. In this paper, we introduce some known map projections from a model of the earth to a flat sheet of paper or map and derive the plotting equations for these projections. So map projections are chosen based on the purposes of the map. Improve your knowledge of map projections in this interactive quizworksheet combo. The perspective point for an orthographic projection is at infinity.
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