(Source: http://www.progonos.com/furuti/MapProj/Normal/ProjTbl/projTbl.htm and Class notes on Map projection).
A globe is the only way to represent the earth with constant scale throughout the entire map in all directions. (Source: ESRI Map projections.pdf). Pseudocylindrical projections represent the central meridian and each parallel as a single straight line segment, but not the other meridians. On the central meridian and the standard latitude shapes are not distorted. Level of expertise required for this Chapter: Advanced Projection parameters use both kinds of descriptions. This pseudocylindrical projection is used primarily as a novelty map. By the geometry of their construction, cylindrical projections stretch distances east-west. This parameter may not be located at the center of the projection. It is most suited for large scale mapping of areas predominantly north-south in extent.
As a world map, this projection maintains equal area despite conformal distortion.Also known as the 'Mercator-Sanson-Flamsteed' projection. You can also use the false easting and northing parameters to reduce the range of the x or y coordinate values. (Source:www.geo.hunter.cuny.edu//Projection%20parameters.htm). 6,356,752 (?) A scale factor of 0.5 means that distance measurements are twice too short.
Unlike a geographic coordinate system, a projected coordinate system has constant lengths, angles, and areas across the two dimensions. These surfaces are cylindrical (e.g. As noted in the introduction, any projection of a sphere (or an ellipsoid) onto a plane will have to distort the image. A projection could maintain the area of a feature but alter its shape. Like the Lambert azimuthal equal-area projection, it is equal area, but it is no longer azimuthal.
This projection preserves the area of individual polygons while simultaneously maintaining true directions from the center. Photographs of Earth (such as those from the International Space Station) give this perspective.
You can also use the false easting and northing parameters to reduce the range of the x or y coordinate values. This projection is similar to the Mercator projection except that the polar regions are not as distorted. This projection is one of the best for middle latitudes. However, this is not attainable over an entire map; it is only correct along certain lines or from a specific point. (In geodesy, plural of "datum" is "datums" rather than "data".)
You can also get some idea of the amount of distortion the projection has added to the data. Fig. The mapping of meridians to vertical lines can be visualized by imagining a cylinder (of which the axis coincides with the Earth's axis of rotation) wrapped around the Earth and then projecting onto the cylinder, and subsequently unfolding the cylinder. However, shapes and distances were distorted.
(www.geo.hunter.cuny.edu//Projection%20parameters.htm). The northing values are measured continuously from zero at the Equator, in a northerly direction.
The various cylindrical projections are distinguished from each other solely by their north-south stretching (where latitude is given by ): In the first case (Mercator), the east-west scale always equals the north-south scale.
It is also possible to define a secant projection by one standard parallel and a scale factor. This causes a distortion in the northern and southern parts of the map, making it appear as if the area of the land in those regions is larger than it actually is. North-south stretching growing rapidly with latitude, even faster than east-west stretching (secant : The cylindric perspective (= central cylindrical) projection; unsuitable because distortion is even worse than in the Mercator projection.
Attribute database | 5.
A projected coordinate system is always based on a geographic coordinate system that is based on a sphere or spheroid. Whether you treat the earth as a sphere or a spheroid, you must transform its three-dimensional surface to create a flat map sheet. The meridians are equally spaced, while the spacing between parallel lines of latitude increases toward the poles. Great circles passing through the focus are represented by straight lines; thus the shortest distance from the center to any other point on the map is a straight line. Penn State Professional Masters Degree in GIS: Winner of the 2009 Sloan Consortium award for Most Outstanding Online Program.
Rather, they depend on mathematical formulae that have no direct physical interpretation.
A pseudo-cylindrical map projection which distorts shape, area, scale and distance to create attractive average projection properties.
(In many world projections, on the other hand, it is defined to be the equator and can't be changed.) Database | Annexes | Site Map, 5.4 Communication with other GIS programs, A2.
The points on the spherical grid are transferred to the cylinder which is then unfolded into a flat plane. This conic projection uses two standard parallels to reduce some of the distortion of a projection with one standard parallel. Directions from the focus are accurate. Each map projection has a set of parameters that you must define. This is the standard parallel.
(ESRI Map projections.pdf), Fig.
GIS for land use planning | 8. The study of map projections is the characterization of these distortions. The shape of the graticule on the flat paper is different from that on the earth. (Source: www.luomus.fi/english/botany/afe/map/utm_ups.pdf). The, For more complex cylindrical projections the cylinder is rotated, thus changing the tangent or secant lines. A surface that can be unfolded or unrolled into a plane or sheet without stretching, tearing or shrinking is called a developable surface. Distortions are are noticeable the further away from the center of the map. Different controls (modifications) are added to the ellipsoid in order to construct the datum, which is specialized for a specific geographic regions (such as the North American Datum). The scale is only accurate along the vertical axis.
The sphere and ellipsoid are not developable surfaces. Tangent and secant are the two types of cases of tangency in cartography. Fig. A standard parallel may or may not coincide with the latitude of origin. 23.6. 23.3. The National Imagery and Mapping Agency (NIMA) (formerly the Defense Mapping Agency) adopted a special grid for military use throughout the world called the Universal Transverse Mercator (UTM) grid. A scale factor of 2.0 means that distance measurements on the map are twice too longif your scale bar tells you it's a hundred kilometers from A to B, it's really only fifty kilometers. As such, their collection depends on the chosen model of the Earth.
A few modern datums, such as WGS84 (the one used in the Global Positioning System GPS), are optimized to represent the entire earth as well as possible with a single ellipsoid, at the expense of some accuracy in smaller regions.
This projection was developed to provide a conformal map of Alaska with less scale distortion than other conformal projections. These are nothing but two big numbers that are added to each x- and y-coordinate, respectively. Maps are created for a variety of purposes, and as a result, there is no single map projection that is better than the rest.
A conformal projection can significantly distort the shape of long geographic features, however within a small area of the point of intersection, the shape will be correct and the scale will be the same in all direction. Conic projections are used for mid latitude zones that have an east-to-west orientation. Every distinct map projection distorts in a distinct way. Fig.
To avoid negative numbers for locations south of the Equator, NIMA's cartographers assigned the Equator an arbitrary false northing value of 10,000,000 meters. Therefore, a map projection must have been used to create the map, and, conversely, maps could not exist without map projections. Secant projections lessen distortion because the globe makes contact with the plane along a line instead of at one point, or makes contact with a 3-D shape along two lines instead of only one. This creates two secant, or standard, lines on the reference globe.
A standard parallel is a line of latitude that has true scale. This modified planar projection shows the true distance from either of two chosen points to any other point on a map. This projection was developed and used by the National Geographic Society for continental mapping. Projections by preservation of a metric property, List of map projections used to represent the Earth's surface, Choosing a model for the shape of the Earth. In other words North can be not be exactly on the top, bottom, left or right side of the map. The Orthographic projection views the earth from an infinite point, as if viewed from deep space. Types of Azimuthal projection based on focus and perspective point. The cylinder, cone and of course the plane are all developable surfaces. This description applies to projections in equatorial aspect. 23.5. This type of projection is usually tangent to the globe at one point but may be secant.
(b) Secant conic projection. Patterns of area and shape distortion are circular about the focus. That is, the plane is normally placed above the north or south pole.
The origin is 49 N and 2 W. The Hammer-Aitoff equal-area projection, also called the Hammer projection, is a map projection that is a modification of the Lambert azimuthal equal-area projection.
Spherical models are useful for small-scale maps such as world atlases and globes, since the error at that scale is not usually noticeable or important enough to justify using the more complicated ellipsoid. These are the standard parallels. This projection is nearly conformal and has little scale distortion within the sensing range of an orbiting mapping satellite such as Landsat. Finally, on the Albers Equal Area Conic projection, the parallels near the northern and southern edges are closer together than the central parallels, and the projection displays equivalent areas (Kennedy, 1994). If you're interested in Australia but you know that a dataset's projection is centered at 0,0, the intersection of the equator and the Greenwich prime meridian, you might want to think about changing the center of the projection. Most map projections can become a secant projection. The parameters specify the origin and customize a projection for your area of interest.
The earth is modeled as a sphere or spheroid.
Selecting a projection such as a conic or polar azimuth enable us to accurately map these regions.
False northing is a linear value applied to the origin of the y coordinates. 23.2. The central point is either the North Pole or the South Pole. Table 23.1. A line of tangency occurs if the globe projects onto a 3-D shape such as a cylinder or a cone from inside, while the globe only contacts the shape along one line. A good way to describe a secant projection is to see what happens when a cylindrical projection becomes a secant projection. This courseware module is part of Penn State's College of Earth and Mineral Sciences' OER Initiative. Lee, L. P. "The Nomenclature and Classification of Map Projections." An azimuthal map projection of the world, centered on Africa. Learn more about the Transverse Mercator projection (. In particular, Conic projections use this parameter to set the origin of the ycoordinates below the area of interest. These are called oblique. (gistutorial.blogspot.com/2011/04/projection-parameters.html). Every x-coordinate is now its original value plus 7,000,000. It may or may not be a line of true scale.
Distortion has less of an impact on certain areas on the map, specifically on and around the secant lines. This azimuthal projection uses the center of the earth as its perspective point. An example of this would be to show the entire area of Japan.
The azimuthal conformal projection, also known as the.
The projections are described in terms of placing a gigantic surface in contact with the earth, followed by an implied scaling operation. This projection is neither equal area nor conformal. Cylindrical projections can also have tangent or secant cases. A map cannot achieve that property for any area, no matter how small. A pseudocylindrical equal-area projection. Home Page | 0. The meridians are equally spaced. The amount of stretch is given by the secant of the latitude as a multiple of the equator's scale. Retrieved September 23, 2017, from, http://www.geo.hunter.cuny.edu/~jochen/gtech201/lectures/lec6concepts/map%20coordinate%20systems/how%20to%20choose%20a%20projection.htm, http://www.progonos.com/furuti/MapProj/Normal/ProjPCyl/projPCyl.html, http://www.geography.hunter.cuny.edu/~jochen/GTECH361/lectures/lecture04/concepts/Map%20coordinate%20systems/Tangents%20and%20secants.htm, http://www.progonos.com/furuti/MapProj/Normal/ProjCon/projCon.html, http://www.gap-system.org/~history/Projects/Hoyer/S5.html, http://www.geography.hunter.cuny.edu/~jochen/GTECH361/lectures/lecture04/concepts/Map%20coordinate%20systems/Classifying%20conic%20and%20pseudoconic%20projections.htm, http://www.geography.hunter.cuny.edu/~jochen/GTECH361/lectures/lecture04/concepts/Map%20coordinate%20systems/Mercator%20projection.htm, http://study.com/academy/lesson/point-of-tangency-definition-example.html, http://geokov.com/education/map-projection.aspx, Paul Anderson's Gallery of Map Projections, Shapefile Projection Finder - Detect the projection of a shapefile, University of Colorado at Boulder - Map Projection Overview with Illustrations, RadicalCartography.net: Table of examples and properties of all common projections, UFF.br: An interactive JAVA applet to study deformations (area, distance and angle) of map projections, Elements of Map Projection with Applications to Map and Chart Construction, U.S. WWII Newsmap, "Maps are Not True for All Purposes, These are three of many projections", BTInternet: Java applet for interactive projections, Geodesy, Cartography and Map Reading from Colorado State University, MapRef: A collection of map projections and reference systems for Europe, PROJ.4 MapTools: Cartographic projections library, GMT (Generic Mapping Tools), for creating maps, processing data, and learning first-hand about projections, B.J.S.Cahill Butterfly Map Resource Page: Octahedral Map of the World, http://wiki.gis.com/wiki/index.php?title=Map_projection&oldid=762728, Cite web templates using unusual accessdate parameters.
The ellipsoidal model is commonly used to construct topographic maps and for other large and medium scale maps that need to accurately depict the land surface. Some map projections are clearly better for specific purposes than others, so the purpose of a map must be considered to determine which projection should be used. The mathematical equations used to transform latitude and longitude coordinates to plane coordinates are called map projections. For example, if you know all y values are greater than 5,000,000 meters, you could apply a false northing of -5,000,000. Shape and linear scale distortion are minimized between the standard parallels. Top: The Cylindrical Equal Area projection has a single standard parallel. None of them are final and official to convert from War Office to UTM 30. Atlas Cartography Geography Map Map projection Topography, Early world maps History of cartography List of cartographers, Cartogram Geologic map Linguistic map Nautical chart Pictorial maps Thematic map Topographic map Weather map, Recommended projections when dealing with hemisphere maps.
A Miller cylindrical projection maps the globe onto a cylinder. False northing is a linear value applied to the origin of the y coordinates. The UNIVERSAL TRANSVERSE MERCATOR is also very widely used.
B. Garo, 1997, Introduction to Map Projections, Arc GIS Online, 8/24/2012, ESRI Publication, (egsc.usgs.gov/isb/pubs/factsheets/fs07701.html) The Universal Transverse Mercator (UTM) Grid, USGS, Fact Sheet 077-01 (August 2001), Projection parameter, GIS Tutorials (gistutorial.blogspot.com/2011/04/projection-parameters.html), Projection parameters (www.geo.hunter.cuny.edu//Projection%20parameters.htm), http://www.progonos.com/furuti/MapProj/Normal/ProjTbl/projTbl.html, Rabu, 2009, GIS Tutorial, For College students Global Mapper GIS, Module 1: Introduction and Concepts of Remote Sensing, Module 2: Sensors, Platforms and Tracking System, Module 3: Fundamentals of Aerial Photography, Module 6: Geographic Information Systems (GIS), Module 10: Fundamentals of Global Positioning System. Annex 8: Map Projection Parameters
This pseudocylindrical projection projection is used primarily for world maps. For this reason, azimuthal projections accommodate circular regions better than rectangular regions. The central meridian is scaled to 0.9996. This projection would be useful in an academic setting where the map is used to measure or compare area.
(Source: www.arcgis.com). With the tangent case Fig. 23.1. This applies for any cylindrical or pseudocylindrical projection in normal aspect. This is the defining characteristic an equidistant projection, such as the, Fran Evanisko, American River College, lectures for Geography 20: "Cartographic Design for GIS", Fall 2002.
Historically, datums have been based on ellipsoids that best represent the geoid within the region the datum is intended to map.
23.8. Choose the Project tool under either the Raster or Feature menu (depending on whether your data is raster or vector), still within the Projections and Transformations toolset. Another way to classify projections is according to properties of the model they preserve. Email gishelp(at)mit.edu for more assistance.
Cylindrical projections map the whole Earth as a finite rectangle, except in the first two cases, where the rectangle stretches infinitely tall while retaining constant width. The meridians are projected onto the conical surface, meeting at the apex, or point, of the cone. The poles are the "normal aspect" (the viewpoint or perspective) which results in the simplest projected grid for this family of projections. The map projection has distorted the graticule. On the Lambert Conic Conformal projection, the central parallels are spaced more closely than the parallels near the border, and small geographic shapes are maintained for both small-scale and large-scale maps.