map distortion types
Some projections minimize distortion or preserve some properties at the expense of increasing distortion of others. The so-called ‘flat-Earth map’ is claimed to be distortion-free, and some flat-Earthers take that as proof of its correctness. Cylindrical map projections are one way of portraying the Earth. It can also be produced in digital form for online use. In addition to the previous distortion types mentioned, which are inherent to the optical design of a lens, improper system alignment can also result in keystone distortion, which is a manifestation of parallax (shown in Figure 7a and 7b). Topo Map Slope an orange peel) onto a flat surface without some stretching, tearing, or shearing. The cylinder may be either tangent or secant to the reference surface of the Earth. )goode projection cuts Antarctica, scientific method of transferring locations on earths surface to a flat map, maintains the shape of landmasses but greatly distorts the water, it argues that the mercator artificially amplifies the size of landmasses to make the nations appear greater. A conformal map distorts area—most features are depicted too large or too small. Carl Friedrich Gauss's Theorema Egregium proved that a sphere's surface cannot be represented on a plane without distortion. Types: Lesson Plans (Individual), Activities, Handouts. In stereographic projections, the perspective point is located on the surface of globe directly opposite from the point of tangency of the plane. The principal scale or nominal scale of a flat map (the stated map scale) refers to this scale of its generating globe. The choice depends on: The location Shape Size of the region to be mapped The theme or purpose of the map 37 38. http://www.youtube.com/watch?v=qgErv6M19yY, http://kartoweb.itc.nl/geometrics/Map%20projections/mappro.html These projections can also be equal area, conformal or equidistant. However the projection of the curved surface on the plane and the resulting distortions from the deformation of the surface will result in variation of scale throughout a flat map. The polar aspect is the normal aspect of the planar projection. No … The ellipses are usually centered at the intersection of meridians and parallels. Some map projections maintain areas, while others preserve local shapes, distances, and directions. The developable surface serves as a good illustrative analogy of the process of flattening out a spherical object onto a plane. They are also used in atlases and thematic mapping. © Eric Gaba – Wikimedia Commons user: Sting. http://www.uff.br/mapprojections/mp_en.html This scale can be measured as the ratio of distance on the globe to the corresponding distance on the Earth. http://www.youtube.com/watch?v=_XQfRYfxPig&feature=related Types of map projections by preserved property (area, shape, direction, distance) Projections are a trade between distortion, accuracy, and aesthetics. Now dot-density maps are also another type of thematic maps. True-direction projections are used in applications where maintaining directional relationships are important, such as aeronautical and sea navigation charts. 1. A scale factor of 1 indicates actual scale is equal to nominal scale, or no scale distortion at that point on the map. The basic problem inherent in any type of map projection is that it will result in some distortion of the ‘ground truth’ of the area being mapped. On a tangent surface to the reference globe, there is no scale distortion at the point (or along the line) of tangency and therefore scale factor is 1. In normal or equatorial aspect, the cylinder is oriented (lengthwise) parallel to the Earth’s polar axis with its center located along the equator (tangent or secant). A developable surface is a geometric shape that can be laid out into a flat surface without stretching or tearing. Choosing a map Projection The choice of map projection is made to give the most accurate possible representation of the geographic information, given that some distortion is inevitable. While pure digital clipping can sound harsh, a dedicated soft/hard clipper can reduce peaks invisibly when used moderately. Along the standard parallel lines in this map (45° N and 45°S), there is no scale distortion and therefore the ellipses would be circular. At the place where the cylinder cuts through the globe two secant lines are formed. Carl Friedrich Gauss's Theorema Egregium proved that a sphere's surface cannot be represented on a plane without distortion. Polyhedral maps can be folded up into a polyhedral approximation to the sphere, using particular projection to map each face with low distortion. In reality, a map can only be distortion-free if the actual shape it represents is also flat. Topographic Maps http://www.btinternet.com/~se16/js/mapproj.htm, "Many ways to see the world": http://www.earthdaytv.net/ Go to "In The Classroom" channel, 4th page http://egsc.usgs.gov/isb/pubs/MapProjections/projections.html It is first accessed when reaching the Spear Pillar, the summit of Mt. 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 map’s scale (distortion is more pronounced in small-scale mapping). Maps do not suffer from the above shortcomings and are more practical than globes in most applications. Geokov Education Once the lens mapping function is known the distortion characteristics are fully determined. Gravity. In gnomonic maps great circles are displayed as straight lines. The shapes of the Tissot’s ellipses in this world map Gall-Peters cylindrical equal-area projection are distorted; however each of them occupies the same amount of area. http://demonstrations.wolfram.com/WorldMapProjections/ Privacy | Disadvantages for maps depicting the entire world with regards to either shape, distance, relative size, and direction. These projections are named azimuthal due to the fact that they preserve direction property from the center point of the projection. They are expensive to produce, especially in varying sizes (scales). When a projection preserves distance, we call it equidistant. Some images used in this set are licensed under the Creative Commons through Flickr.com.Click to see the original works with their full license. The good news is that map projections allow us to distort systematically; we know exactly how things are being stretched or squashed at any given point. Compass Basics by . ciﬁc image distortion types, viewing environments and inex-perienced viewers. Dot-density maps usually use dots to represent the volume or density of a certain factor like population. The properties of area, distance, and form are mutually exclusive. The Robinson projection balances area and shape distortion. Notice that the shapes of the ellipses in the Cylindrical Equal Area projection above (Figure 2.29.1) are distorted, but the areas each one occupies are equivalent. As an example, the actual scale at a given point on map with scale factor of 0.99860 at the point and nominal map scale of 1:50000 is equal to (1:50000 x 0.99860) = (0.99860 / 50000) = 1:50070 (which is a smaller scale than the nominal map scale). Maps continue… 1) Map scale – most maps are smaller than the reality they represent & map scale tells us how much smaller; tells relationship between distance on map and distance on Earth’s surface 2) Map type – you can display the same information on different types of maps ex. In orthographic projections, the point of perspective is at infinite distance on the opposite direction from the point of tangency. http://www.giss.nasa.gov/tools/gprojector/ Transverse and oblique aspects are seldom used. In equidistant map projections, accurate distances (constant scale) are maintained only between one or two points to every other point on the map. when talked about as a whole. Maintaining relative areas of features causes distortion in their shapes, which is more pronounced in small-scale maps. For the polar or normal aspect, the cone is tangent along a parallel of latitude or is secant at two parallels. http://www.ec-gis.org/sdi/publist/pdfs/annoni-etal2003eur.pdf Distance and shape distortion increase sharply by moving away from the center of the projection. In conical or conic projections, the reference spherical surface is projected onto a cone placed over the globe. Plate carrée is a case of equirectangular projection with Equator being a standard parallel. A type of projection can be suitable for a purpose but not for others. Map distortion glitch types are glitch types capable of map corruption due to a buffer overflow. The cone can be situated over the North or South Pole. The Robinson projection is unique. Preservation of angles makes conformal map projections suitable for navigation charts, weather maps, topographic mapping, and large scale surveying. Some examples are Albers Equal-Area Conic, Cylindrical Equal Area, Sinusoidal Equal Area, and Lambert Azimuthal Equal Area projections. This aspect produces a map with meridians radiating out as straight lines from the cone’s apex, and parallels drawn as concentric arcs perpendicular to meridians. The diameter of the cylinder is equal to the diameter of the globe. Gall-Peters cylindrical equal-area projection Tissot's indicatrix In transverse aspect of conical projections, the axis of the cone is along a line through the equatorial plane (perpendicular to Earth’s polar axis). This type of map is also known as “reference map” and is either printed on a physical medium or paper. Tap card to see definition . In other words the actual map scale is different for different locations on the map plane and it is impossible to have a constant scale throughout the map. The only factor that distinguishes different cylindrical map projections from one another is the scale used when … Contour Lines - Terrain 2 Distances measured along these lines are proportional to the same distance measurement on the curved reference surface. There is great distortion towards the borders of the map. These parallels are called standard parallels. As a result, a map using this projection has distortions in distances, shapes, directions, and areas. http://demonstrations.wolfram.com/DistortionsInMapProjections/ Azimuthal projections are used often for mapping Polar Regions, the polar aspect of these projections are also referred to as polar azimuthal projections. About, Gall-Peters cylindrical equal-area projection Tissot's indicatrix, Mercator - conformal projection Tissot's indicatrix, Equirectangular (equidistant cylindrical) projection Tissot's indicatrix. Conic projection - tangent and secant © USGS. The map resorts to mathematics to curtail three major types of distortion – area, direction, and distance (and hence the German term for ‘triple’, Tripel, is in the name). A… Scale is true (scale factor = 1) and there is no distortion along standard parallels. Maybe you want to compare the distortions which are present in each and every map projection. As the name suggests, a dot distribution map is a type of map that uses dot symbols to indicate the presence of features and depends on visual scatters to show spatial patterns. The map projections with the least distortion will have the smallest gaps when folded into a sphere, while map projections with a lot of di. As stated above spherical bodies such as globes can represent size, shape, distance and directions of the Earth features with reasonable accuracy. Shape of an area can be distorted ex. The same applies to other reference surfaces used as models for the Earth, such as oblate spheroids, ellipsoids and geoids.Since any map projection is a representation of one of those surfaces on a plane, all map projections distort. From Glitch City Wiki. On a curved surface, measuring terrain properties is difficult, and it is not possible to see large portions of the Earth at once. Very lately, Ponomarenko et al. https://courseware.e-education.psu.edu/projection/index.html, Site Map | We have many different map projections because each has different patterns of distortion—there is more than one way to flatten an orange peel. Projections can be further categorized based on their point(s) of contact (tangent or secant) with the reference surface of the Earth and their orientation (aspect). Meridians and parallels are perpendicular to each other. These maps also use dots to show the distribution of … The cone may be either tangent to the reference surface along a small circle (any circle on the globe with a diameter less than the sphere’s diameter) or it may cut through the globe and be secant (intersect) at two small circles. Their shape represents the distortion of an imaginary circle on the spherical surface after being projected on the map plane. In this world map equidistant cylindrical projection (also known as plate carrée), Tissot’s ellipses are distorted in size and shape. Mercator maps are used in navigation because a line drawn between two points of the Earth has true direction. No map can be both conformal and equal area. Knowledge of these different advantages and disadvantages for a particular map projection will often help in which map to choose for a particular project. They are hard to transport and store; for example you can not stuff a globe in your backpack while hiking or store it in your car’s glove compartment. A feature that has made Mercator projection especially suited for nautical maps and navigation is the representation of rhumb line or loxodrome (line that crosses meridians at the same angle) as a straight line on the map. Features appear smaller between secant lines (scale < 1) and appear larger outside these lines (scale > 1). The Mercator projection, for example, distorts Greenland because of its high latitude, in the sense that its shape and size are not the same as those on a globe. In this aspect the cone’s apex is situated along the polar axis of the Earth, and the cone is tangent along a single parallel of latitude or secant at two parallels. Distortion increases by moving away from standard lines. Map Projections Basic Principles. 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