In this chapter, we will seek the answers of such essential questions. Map projections chapter 4 map projections what is map projection. Map projection definition of map projection by the free. It was created by flemish cartographer gerardus mercator in 1569 a time when antarctica hadnt even been discovered. The albers equal area conic projection is commonly used for the united states. Which projection is most suitably used for which area. May 25, 2015 the straight lines approach is so useful for travel that the mercator projection has also made its way onto the most popular digital maps websites. This is a summary of map projections that have articles of their own on wikipedia or that are otherwise notable.
Unlike conic projections, the meridian is not constrained to be a straight line. Mercator was designed as a navigational tool for sailors as it was most convenient to handplot courses with parallel rules and triangles on this map. Small area life expectancy estimates project usaleep is a partnership of nchs, the robert wood johnson foundation rwjf external icon, and the national association for public health statistics and information systems naphsis external icon to produce a new measure of health for where you live. On the other hand, one kind of projection that doesnt distort area is the cylindrical equal area. This equal area projection is useful when mapping large ocean areas.
Pseudoconic projection is one of the oldest map types and although they were used by ptolemy, they are seldom seen today. If a map passes the penny test it is called an equal. Ap human geography types of map projections 12 terms. When a map preserves shape over a small area it is said to be conformal orthomorphic right in greek. Equal area projections are preferred for small scale thematic mapping discussed in the next chapter, especially when map viewers are expected to compare sizes of area features like countries and continents.
However, map projections have distortions which depend largely on the size of the area being mapped. Examples of pseudoconic projections include bonne, which is an equal area map projection. Map projections designed for small scale data are usually based on spherical rather than spheroidal geographic coordinate systems. This is the most profound single fact about map projections they distort the worlda fact that you will investigate in more detail in module 4, understanding and controlling distortion. Vertical axis modified so that within a small area vertical and horizontal scales the same trick ensure directional vectors all the same. Because there is no limit to the number of possible map projections, there can be no comprehensive list. Map projection is a very complex topic and we cannot cover it completely here. The mollweide projection is an equal area, pseudocylindrical map projection generally used for global maps of the world or night sky. A map projection is a geometric function that transforms the earths curved, ellipsoidal surface onto a flat, 2dimensional plane. The old latitude rule has been given a new formulation by frank canters, author of small scale map projection design, in slightly different words than these. That is to say, australia is three times as big as greenland. It looks similar to the widely used robinson projection, but unlike the robinson projection, retains. Even though it is nearly impossible to create an entirely accurate map projection there are uses for even the most imperfect depictions of the earth. Another example is the robinson projection, which is often used for small scale thematic maps of the world it was used as the primary world map projection by the national geographic society from 19881997, then replaced with another compromise projection, the winkel tripel.
Notice here how greenland looks the right size as compared to south america. They then examine the distortions of different map projections while comparing land and ocean to its representation on a globe. A map projection either preserves areas everywhere, or distorts it everywhere. Geological survey usgs now uses several of the more common projections for its published maps. Planar a map projection resulting from the conceptual projection of the earth onto a tangent or secant plane. Dec 27, 2002 a map projection is one of many methods used to represent the 3dimensional surface of the earth or other round body on a 2dimensional plane in cartography mapmaking. The request for small area distortion is typical for e. The stereographic map projection is another ancient projection, dating back to the second century b.
This projection is not equal area, and shapes in the outer half are greatly distorted. Maps and map projections maps can be reproduced easily, can depict the entire earth or show a small area in great detail, are easy to handle and transport, and can be displayed on a computer monitor. A map projection is used to portray all or part of the round earth on a flat. The great attraction of the projection is that the earth appears as if viewed form space or a globe.
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. All projections of a sphere on a plane necessarily distort the surface in some way and to some extent. The usaleep project produced estimates of life expectancy at birththe average number. The scale, however, varies with the distance from that point. One map projection might be used for largescale data in a limited area, while another is used for a small scale map of the world.
Local maps for maps of cities or small regions, the choice is easy. Conformality distortion ellipses on a mercator projection the. Lecture 2 map projections and gis coordinate systems. For small areas, the overall distortion is minimal. It is the representation of the objects and information on a curved surface in a plane using mathematical and geometric relations. On these, the shapes of small areas are shown correctly, but scale is correct only along one or two lines.
Vice versa, an area preserving projection can not be conformal, resulting in shapes and bearings distorted in most places of the map. Considerations for small scale gis applications by eric m. Map projection a map projection is a systematic transformation of the latitudes and longitudes of locations on the surface of a sphere or an ellipsoid into locations on a plane. Each projection preserves, compromises, or approximates basic metric properties in different ways. Many small scale map projections exist, and they have different shapes and.
Antiti map types and properties tn 7 a map is a representation of all or part of the earth drawn on a flat surface at a specific scale. They lie between 65000n and 831500n and approx 64w and 93w. The map on the left is a mollweide equal area projection which preserves the relative area of landforms. Map projection category maintained distorted equivalent equal area areal scale angle, shape, distance equidistant distance over some portions direction, area azimuthal angular relationships from a central point shape, distance, area conformal small shapes and because of that angles as well large area map projection categories and resulting. Map projections are designed for specific purposes. Any projection can have either conformal property or equal area property, but not both.
Map projections without distortions would represent the correct distance, direction, shapes, and areas on a map. Today the lambert conformal conic projection has become a standard projection for mapping large areas small scale in the mid. Map projection academic dictionaries and encyclopedias. Equal earth map projection meets cartographic needs and desires. 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. Converting a sphere to a flat surface results in distortion. A projected coordinate system based on a map projection such as transverse mercator, albers equal area, or robinson, all of which along with numerous other map projection models provide various mechanisms to project maps of the earths spherical surface onto a twodimensional cartesian coordinate plane. Map projection map projection is the method of transferring the graticule of.
Map projection types all have their pros and cons, but they are incredibly versatile. Many important persons gave their contribution to development of theory and practice of map projections through the history. The mollweide projection is an equalarea, pseudocylindrical map projection generally used for global maps of the world or night sky. While no universally accepted definition exists for what constitutes a small area for population estimation and projection purposes, it commonly involves administrative units below the national and state level. In cartography, a map projection is a way to flatten a globes surface into a plane in order to make a map. After decades of using only one map projection, the polyconic, for its mapping program, the u. The azimuthal equidistant map projection is useful because it can be centered on one city, for example, showing airline distances from that point. A guide to selecting map projections for world and hemisphere maps. Jul 03, 20 i would like to check that i am using the most appropriate map projection for some area calculations. The usaleep project produced estimates of life expectancy at birththe. Map projections page 7 map scale a u s t r a l i a example of a small scale map the scale field at the bottom of tnt view windows shows the map scale at the current zoom level for the georeferenced data you are viewing.
Estimates and projections for small areas, in particular, are used extensively in the public and private sectors. Map projection that shows shapes accurately over small areas is called a. Stereographic projection an overview sciencedirect topics. 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.
The maps are not constrained to rectangles or discs. The choice of a projection for a map depends on such factors as the purpose for which the map will be used, the area being mapped, and the maps scale distortion is more pronounced in smallscale mapping. There are many different varieties of maps, and they all have qualities that can be either advantageous or problematic, depending on the application. To map areas that extend along a great circle, use a cylindrical projection to map areas that extend along a small circle, use a conic projection. Nvss united states smallarea life expectancy estimates project. A coordinate system, datum, and map projection are. A stereographic projection, or more simply a stereonet, is a powerful method for displaying and manipulating the 3dimensional geometry of lines and planes davis and reynolds 1996. Maps use a variety of symbols and colours to represent selected features of an area. Investigating map projections students use oranges to investigate the effects of changing a 3d surface to a 2d surface. Smallarea estimates and projections population estimates and projections play a critical role in market analysis, facility planning, environmental planning, and the allocation of public and private funds.
Maps were devised because they are much easier to use, store, and transport than globes, and they facilitated the development of much larger. Conformal projections preserve angles, and are useful for navigational charts and weather maps. 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. A map projection where every part, as well as the whole, has the same area as the corresponding part on the earth, at the same reduced scale. This is useful for analysis involving areas like the size of the property, e. An equal area map which shows the correct size of landmasses in relation to other landmasses but distorts shape. When people search for places or plan routes with map apps the area shown is usually relatively small enough to be unaffected by any distortion.
Apr 25, 2017 examples of pseudoconic projections include bonne, which is an equal area map projection. This chapter focuses on projections for world and hemisphere. There are a number of techniques for map projection, yet in all of them distortion occurs in length, angle, shape, area or in a combination of these. The equal earth map projection is a new equal area pseudocylindrical projection for world maps. This means that the shapes of small areas are maintained accurately.
Manual by lev bugayevskiy and john snyder, ball state. Map projection means representing a portion of the actual earth on a plane. Equal area map projections also known as equivalent or authalic projection represent areas correctly on the map. Map projections distort angles, areas and distances. The projection on the right is a gall projection very similar to a mercator projection, and it preserves the shape of landforms but not the area. An example of a polar azimuthal equidistant map projection can be seen on the united nations flag. I need to run some area calculations for large features in northern canada. Map projections map, department of the interior, u. As mentioned above, the correctness of area, shape, direction and distances are the four major global properties to be. Over a small geographic area the distortions caused by the map projection are not significant, but the selection of an appropriate map projection is crucial for larger regions. European commission joint research centre 2001 eur 20120 en institute for environment and sustainability map projections for europe edited by. The most popular map projection in the world has been around for 448 years now.
Investigating map projections national geographic society. A small map that depicts a large area has a small scale fraction. Map projection classifications based on physical surface models. The drawback of this projection is that things near the poles appear too big and things near the equator appear too small. The intersection made by the line or plane with the spheres.
Jun 06, 2017 the map scale may be expressed in three ways and the pictorial representation of these three types is shown in the figure. It is also known as the babinet projection, homalographic projection, homolographic projection, and elliptical projection. Imagine a map projection as an attempt to reconstruct your face in two dimensions. State plane coordinate systems are built on map projections. 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. The areas of features on the map are proportional to their areas on the reference surface of earth.
Arno peters, a german historian and journalist, in 1973. The purpose of the map determines which projection should form the base for the map. About a week after these stories started to appear in the news, tom patterson, a cartographer who has since retired from the us national park service, began looking at equalarea projections to identify an alternative to gallpeters. Transverse mercator map of a small area in the same high latitudes. His major aim in developing this projection was to create a map on which the size of countries were accurately represented unlike on the mercator projection.
The lambert azimuthal equal area map projection was developed by johann lambert in 1772. Although the earth is best represented by a spheroid, the earth is sometimes treated as a sphere. Delmelle a project submitted to the faculty of the graduate school of state university of new york at buffalo in partial fulfillments of. Projections which preserve areas are called equivalent or equalarea projections. A projection showing accurate areas is called an equal area map. Showing different kinds of phenomena on maps is called. Businesses survey of business owners survey of income and program participation. Map projections and distortion city university of new york. If it is tangential to a point between the pole and the equator, it is called the oblique projection. Although the earth is best represented by a spheroid, the earth is sometimes treated as a sphere to make mathematical calculations easier. The orientations of lines and planes can be plotted relative to the center of a sphere, called the projection sphere, as shown at the top of fig. Maintaining relative areas of features causes distortion in their shapes, which is more pronounced in small scale maps.
In all cases, the shape of continental areas is altered and deforms the message the map is meant to communicate, especially for small scale maps. It allows the reader to see quickly, if one map can be compared with another. In very large areas small scale, on the other hand, distortion is a more important factor to consider. 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. The equal earth projection maintains the true relative sizes of the earths features and is visually pleasing. Small area demography refers to demographic applications and analyses executed at local and regional scales smith and morrison, 2005. Nvss united states smallarea life expectancy estimates. The stereographic map projection is conformal but not. This requires a systematic transformation of the latitudes and longitudes of locations from the surface of the globe into locations on a plane. Thus, any map projection causes distortion in the shape, area, distance, scale or direction of the data. However, using the proper map projection will depict the. As long as the area of interest is small, this will. Scale decreases away from the center point, as distortion of shapes increases.
To discuss this subject the joint research centre asked eurogeographics to organise a second workshop in december 2000 which the main objective was to analyse the european commission primary needs for map projections and obtain expert advice to select an appropriate set of european conventional reference. A map projection is used to portray all or part of the round earth on a flat surface. Globes and traditional paper maps depict scaleddown versions of surface features. On small areas large scale data compatibility issues are more important since metric distortions are minimal at this level. It is most commonly used over polar areas, but can be used for small scale maps of continents such as australia. Shape flat maps cannot depict large regions of earth without distorting either their shape or their comparative sizes in terms of area. Advances in smallscale map projection research openedition. 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.
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