an orange peel) onto a flat surface without some stretching, tearing, or shearing. Planar (azimuthal) projection - tangent and secant © USGS. Geokov Map maker Even on a conformal map, shapes are a bit distorted for very large areas, like continents. http://www.radicalcartography.net/index.html?projectionref If you have a map projection that preserves one, it will distort the other two But, these maps use dots instead of lines, shapes and colors. The size, shape and orientation of the ellipses are changed as the result of projection. Here the area distortion is more pronounced as we move towards the poles. The plane in planar projections may be tangent to the globe at a single point or may be secant. km) on the globe represents 250000 units on Earth. 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. But this is not the case as the Earth is a sphere. The best way to describe how a map projection works is by imagining a piece of paper (the map) being laid over the Earth (or a globe) to obtain the latitude and longitude lines for the map. Scale is true (scale factor = 1) and there is no distortion along standard parallels. The resulting map from this projection looks like a globe (similar to seeing Earth from deep space). 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. Types of Map Projections Cylindrical . The ellipses show how imaginary circles on the globe are deformed because of a particular projection. The tangent line is the equator for the equatorial or normal aspect; while in the transverse aspect, the cylinder is tangent along a chosen meridian (i.e. Great circles are the shortest distance between two points on the surface of the sphere (known as great circle route). Shape of an area can be distorted ex. http://www.youtube.com/watch?v=qgErv6M19yY, http://kartoweb.itc.nl/geometrics/Map%20projections/mappro.html In gnomonic maps great circles are displayed as straight lines. http://www.csiss.org/map-projections/, USGS Decision Support System: http://mcmcweb.er.usgs.gov/DSS/ it measures highest to 90 degrees at the north pole or 90 degrees at the south pole, lines of longitude are called meridians. Directions are true from the center point (North Pole). A map derived from a secant projection surface has less overall distortion than a map from a tangent surface. Critics of the map – and similar projections – suggest that distortion reinforces a sense of colonialist superiority. Gnomonic projections map all great circles as straight lines, and such property makes these projections suitable for use in navigation charts. It is first accessed when reaching the Spear Pillar, the summit of Mt. So what a cartogram does is that it takes some statistical data and then combines it with the given area by distorting it to reflect the data. In equidistant map projections, accurate distances (constant scale) are maintained only between one or two points to every other point on the map. 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. This can be alternatively stated as ratio of distance on the map to the corresponding distance on the reference globe. 3 Experimental results This would mean that features lying on the 20th parallel are equally distorted, features on the 40th parallel are equally distorted … As stated above spherical bodies such as globes can represent size, shape, distance and directions of the Earth features with reasonable accuracy. Map Distortion. An equal-area map projection that is an ellipse. In this world map equidistant cylindrical projection (also known as plate carrée), Tissot’s ellipses are distorted in size and shape. Polyhedral maps can be folded up into a polyhedral approximation to the sphere, using particular projection to map each face with low distortion. Sometimes, two map projections might look so similar that it’s hard to tell the difference. These maps also use dots to show the distribution of … http://www.uff.br/mapprojections/mp_en.html cific image distortion types, viewing environments and inex-perienced viewers. Latitude and Longitude Distortion ellipses help us to visualize what type of distortion a map projection has caused, how much distortion occurred, and where it occurred. by . Robinson Projection. However shapes of large areas do get distorted. During such transformation, the angular geographic coordinates (latitude, longitude) referencing positions on the surface of the Earth are converted to Cartesian coordinates (x, y) representing position of points on a flat map. The tangent and secant lines are important since scale is constant along these lines (equals that of the globe), and therefore there is no distortion (scale factor = 1). In the tangent case, the cylinder’s circumference touches the reference globe’s surface along a great circle (any circle having the same diameter as the sphere and thus dividing it into two equal halves). https://courseware.e-education.psu.edu/projection/index.html, Site Map | Globes are not suitable for use at large scales, such as finding directions in a city or following a hiking route, where a more detailed image is essential. No flat map can be free of all 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. In the secant case the plane intersects the globe along a small circle forming a standard parallel which has true scale. Click card to see definition . Measure of scale distortion on map plane can also be quantified by the use of scale factor. released the TID2013 [11], which is up to now the largest image quality database consisting of totally 3000 distorted images. Map scale distortion of a secant cylindrical projection - SF = 1 along secant lines, Scale distortion on a secant surface to the globe. Although for many mapping applications the earth can be assumed to be a perfect sphere, there is a difference between the distance around the earth between the poles versus the equator. 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). http://mathworld.wolfram.com/topics/MapProjections.html The plane is tangent to North or South Pole at a single point or is secant along a parallel of latitude (standard parallel). 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. maps 256 feature maps 128 feature maps 128 feature maps 192 conv max pooling incption conv max pooling fc concat conv max pooling incption conv max pooling fc CNN-putput putput weight Hue Image Gray Image Test Image Saliency map F :Algorithmarchitecture. Distortion increases by moving away from standard parallels. Azimuthal projections are used often for mapping Polar Regions, the polar aspect of these projections are also referred to as polar azimuthal projections. The two axes of the ellipse indicate the directions along which the scale is maximal and minimal at that point on the map. Different projections are developed for different purposes. Some classic azimuthal projections are perspective projections and can be produced geometrically. Examples of equidistant projections are azimuthal equidistant, equidistant conic, and equirectangular projections. Its primary purpose is to create visually appealing maps of the entire world. 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). The only factor that distinguishes different cylindrical map projections from one another is the scale used when … Topographic Maps 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). Contact Us | The amount of distortion, however, is regular along some lines in the map. When a projection preserves distance, we call it equidistant. http://egsc.usgs.gov/isb/pubs/MapProjections/projections.html Pseudoconic projection is one of the oldest map types and although they were used by Ptolemy, they are seldom seen today. http://www.youtube.com/watch?v=e2jHvu1sKiI&feature=rec-LGOUT-exp_fresh+div-1r-3-HM The concept of distortion describes how a lens maps a shape on the object plane to the image plane while assuming other aberrations are negligible. The cone can be situated over the North or South Pole. Stereographic projection is a conformal projection, that is over small areas angles and therefore shapes are preserved. In transverse aspect, the cylinder is oriented perpendicular to the Earth’s axis with its center located on a chosen meridian (a line going through the poles). This variation of scale can be visualized by Tissot's indicatrix explained in detail below. thematic, dot, cartogram, etc. Knowledge of these different advantages and disadvantages for a particular map projection will often help in which map to choose for a … Mercator Projection. Map distortion glitch types are glitch types capable of map corruption due to a buffer overflow. http://www.youtube.com/watch?v=2LcyMemJ3dE&feature=related At the place where the cylinder cuts through the globe two secant lines are formed. Geokov Education http://www.flexprojector.com/ Some examples are Albers Equal-Area Conic, Cylindrical Equal Area, Sinusoidal Equal Area, and Lambert Azimuthal Equal Area projections. Distance between points may become increased or decreased ex. 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. Match. Sometimes, you might see the difference but want to study it more closely. Robinson projection © Eric Gaba – Wikimedia Commons user: geographic coordinates (latitude, longitude), http://egsc.usgs.gov/isb/pubs/MapProjections/projections.html, http://webhelp.esri.com/arcgisdesktop/9.2/index.cfm?TopicName=List_of_supported_map_projections, http://www.radicalcartography.net/index.html?projectionref, http://en.wikipedia.org/wiki/List_of_map_projections, http://www.colorado.edu/geography/gcraft/notes/mapproj/mapproj_f.html, http://mathworld.wolfram.com/topics/MapProjections.html, http://www.giss.nasa.gov/tools/gprojector/, http://www.uff.br/mapprojections/mp_en.html, http://demonstrations.wolfram.com/WorldMapProjections/, http://demonstrations.wolfram.com/DistortionsInMapProjections/, http://www.btinternet.com/~se16/js/mapproj.htm, http://www.youtube.com/watch?v=2LcyMemJ3dE&feature=related, http://www.youtube.com/watch?v=e2jHvu1sKiI&feature=rec-LGOUT-exp_fresh+div-1r-3-HM, http://www.youtube.com/watch?v=_XQfRYfxPig&feature=related, http://www.youtube.com/watch?NR=1&v=EPbQQNrBIgo, http://www.youtube.com/watch?v=AI36MWAH54s&feature=related, http://www.youtube.com/watch?v=b1xXTi1nFCo, http://www.youtube.com/watch?v=qgErv6M19yY, http://kartoweb.itc.nl/geometrics/Map%20projections/mappro.html, http://www.progonos.com/furuti/MapProj/Normal/TOC/cartTOC.html, Map Projections - A Working Manual (USGS PP 1395, John P. Snyder, 1987), http://www.ec-gis.org/sdi/publist/pdfs/annoni-etal2003eur.pdf, https://courseware.e-education.psu.edu/projection/index.html.