The mercator projection is a useful navigation tool, as a straight line on a mercator map indicates a straight course, but it is not a practical world map, because of distortion of scale near the poles. No projection allows us to flatten the globe without distorting it. The ellipses show how imaginary circles on the globe are deformed because of a particular. Distortion ellipses help us to visualize what type of distortion a map projection has caused, how much distortion occurred, and where it occurred. To represent parts of the surface of the earth on a flat paper map or on. The straight lines crossing at right angles of this map projection make it useful for navigation, but it distorts. The mercator projection is a cylindrical projection that was developed for navigation purposes. Mercator projection, a map projection introduced by flemish cartographer gerardus mercator in 1569. Mercator projection an overview sciencedirect topics. The central focus of this book is on the theory of map projections. Imagine the earths surface is clear with the graticuledrawn on it.
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. Depending on the purpose of the map, some distortions may be less bad. About map projectionthe classification of map projection. The earths surface projected on a map wrapped around the globe as a cylinder produces the cylindrical map projection. They can be used to measure areas, or distances, and they can show the best route from one place to another. The mercator projection is still commonly used for areas near the equator, however, where distortion is minimal. This mathematical transformation is commonly referred to as a map projection. These maps will focus on an important location as their central point and use an appropriate aspect. Map projection simple english wikipedia, the free encyclopedia. Map projections explained a beginners guide youtube. Because there is no limit to the number of possible map projections, there can be no comprehensive list.
Projection techniques for document maps moritz stefaner. A medieval depiction of the ecumene 1482, johannes schnitzer, engraver, constructed after the coordinates in ptolemys geography and using his second map projection. Lecture 2 map projections and gis coordinate systems. This booklet provides a conceptual introduction to map projections and geographic reference systems. As a result of these criticisms, modern atlases no longer use the mercator projection for world maps or for areas distant from the equator, preferring other cylindrical projections, or forms of equalarea projection. A sphere, unlike a polyhedron, cone, or cylinder, cannot be reformed into a plane. Electronic navigation enav systems together with specific.
Using a cylinder and a globe with light is a simplified explanation as to how the mercator projection works. The stereographic map projection is another ancient projection, dating back to the second century b. This is a summary of map projections that have articles of their own on wikipedia or that are otherwise notable. Pdf map projections and visualization of navigational paths in. Mercator map enthusiasts defend the ease of navigation of their map. The cone is so positioned that it cuts into the earth at one parallel and comes out again at a parallel closer to.
Jan 06, 2017 learn what a map projection is, why they are used and what impact they have on maps gis systems. Circumference of lines of latitude getting smaller, map s width staying constant. Nov 21, 2019 proponents of the peters projection map claim that their map is an accurate, fair, and unbiased depiction of the world when comparing theirs to the almostdefunct mercator map, which features enlarged depictions of eurocentric countries and continents. Media in category maps of the world with mercator projection the following 59 files are in this category, out of 59 total. We examine how to map spherical and ellipsoidal earth onto 2dimensional space, and compare two paths one can take between two points on the earth. When you switch from one projection to another, setm clears out settings that were specific to the earlier projection, updates the map frame and graticule, and generally keeps the map covering the same part of the worldeven when switching between azimuthal and nonazimuthal projections. Done for hundreds of years to create paper maps, it continues, but map projection today is most often really a mathematical procedure done in a computer. In the process of projection the earth is represented by a model an ellipsoid. Map projections used in polar regions the journal of. Clearly, the automization of a very specialized skill like cartography requiring high technical, aesthetical and empathic capabilities on side of the mapmaker is not an easy projection techniques for document maps 9. This requires a systematic transformation of the latitudes and longitudes of locations from the surface of the globe into locations on a plane. 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. This map projection is practical for nautical applications due to its ability to represent lines of constant course, known as rhumb lines, as straight segments that conserve the angles with the meridians.
But in some cases, you might need to further adjust the. The mercator projection was used for its portrayal of direction and. One easy way to understand how map projections alter spatial properties is to visualize shining a light through the earth onto a surface, called the projection surface. Map projection distorts reality a sphere is not a developable solid. Map projection is the method of transferring the graticule of latitude and longitude on a. A description of how cylindrical projections are developed. The geoid is defined as the surface of the earths gravity field, which is approximately the same as mean sea level. This paper provides an overview of the mercator map projection. Lambert conformal projection, conic projection for making maps and charts in which a cone is, in effect, placed over the earth with its apex aligned with one of the geographic poles.
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. Media in category maps with robinson projection the following 200 files are in this category, out of 272 total. Oct 01, 2015 in this series, we talk about the basics of map projections, including coordinate systems and datums. The mercator projection is a cylindrical map projection presented by the flemish geographer and cartographer gerardus mercator in 1569. In looking at these two paths, we will investigate how latitude and longitude play an. Maps can display true courses for navigation and accurate shapes of earth features. Lambert conformal projection topography britannica. A map projection is used to portray all or part of the. The mercator projection was used for its portrayal of direction and shape, so it was helpful to the sailors of that time.
It is perpendicular to the direction of gravity pull. However, using the proper map projection will depict the. A guide to selecting map projections for world and hemisphere maps. This chapter provides guidance in selecting projections for world and hemisphere maps. Although the earth is best represented by a spheroid, the earth is sometimes treated as a sphere to make mathematical calculations easier.
The mercator projection is a useful navigation tool, as a straight line on a mercator map indicates a straight course, but it is not a practical world map, because. It is also a conformal projection that preserves angles and a linear point scale that is equal in all directions around any point. Map projections used in polar regions volume 6 issue 1 p. We will taker a closer look at the popular mercator projection and examine how the projection. A map projectionis a mathematically described technique of how to represent the earths curved surface on a flat map. Map projection means representing a portion of the actual earth on a plane. Therefore it is not imperative to adopt the mercator or gnomonic projections as in traditional navigation. A map projection is a way of showing the surface of a threedimensional sphere on a flat surface. In order to portray the surface of a round body on a twodimensional flat plane, you must first define a developable surface i. 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. Pdf a guide to selecting map projections for world and.
The field of map projections concerns itself with the ways of translating the curved surface of the earth into a flat map. Want to know how cartographers make 2d maps of our 3d planet. In cartography, a map projection is a way to flatten a globes surface. Map projections distortions projection refers to the notion of shining light through the earth surface and projecting latitudes, longitudes and geographic features onto a developable surface. The problem with projections is that they change the surface in some way. Because earth has a curving, notquite sphericial shape, planar maps of. Map projections page 3 introduction to map projections although earth images and map data that you use are typically rendered onto flat surfaces such as your computer screen or a sheet of paper, the earths surface obviously is not flat. The azimuthal map projection is angular given three points on a map a, b, and c the azimuth from point b to point c dictates the angle someone would have to look or travel in order to get to a.
Although the projection procedure inevitably introduces systematic spatial distortions, particular types of distortion can be minimized to suit the geographic scope and intended use of the map data. This means different y scales in different parts of the map what is the xscale factor. A map projection is a systematic transformation of the latitudes and longitudes of positions on the surface of the earth to a. This makes the mercator projection very useful in world navigation and was used by early sailors in their explorations and discoveries of new continents. A map projection is a way to flatten a globes surface into a plane in order to make a map. Given a cylindrical projection, the x scale must increase away from equator. The three classes of map projections are cylindrical, conical and azimuthal. Jan, 2014 instead they could mark their starting and ending points and simply follow the line along their expeditions. Implementation practice web mercator map projection.
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