Understanding map projections melita kennedy, steve kopp. Map projections try to portray the surface of the earth or a portion of the earth on a flat piece of paper or computer screen. Gis data typically uses the 2d cartesian coordinate system for simplicity. 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. Projections going from 3d to flat maps understanding coordinate. If you like, the next step on from understanding that the shape of the earth is round rather. Page 79 discuss map scale and the basics of coordinate systems. World geodetic system wgs, and for converting cartesian and map projection coordinates to and from geodetic coordinates.
Understanding datums, coordinate systems and map projections. Understanding difference between coordinate system and. A gis without coordinates would simply be a database like microsoft excel or access. Understanding coordinate systems and map projections pdf. Projected coordinate systems a map projection is the systematic transformation of locations on the earth latitudelongitude to planar coordinates the basis for this transformation is the geographic coordinate system which references a datum map projections are designed for specific purposes. All projections of a sphere on a plane necessarily distort the surface in some way and to some extent. Coordinate systems, map projections, and geographic datum. Handbook for transformation of datums, projections, grids.
The course format includes detailed information on how these concepts are applied to. Their purpose is to provide a common basis for communication about a particular place or area on the earths surface. A coordinate reference system crs then defines, with the help of coordinates, how the twodimensional, projected map in your gis is related to real places on the earth. The shape of the earth and the geodetic datum concept are covered on pages 46. A gcs is often incorrectly called a datum, but a datum is only one part of a gcs. In this series, we talk about the basics of map projections, including coordinate systems and datums. A geographic coordinate system is a coordinate system that enables every location on earth to be specified by a set of numbers, letters or symbols. Just as all maps have a map scale, all maps have locations, too. Map projections are introduced on pages 1012, and pages.
Since the planet earth isnt flat, some distortions ofthe data will inevitably occur during the transformation process. Even if a 2d coordinate system includes height, or elevation information, it is still assumed to be a height above a flat plane. Defining coordinates for the earths surface is complicated by three main factors. Whenever you make a map, youre abstractinginformation about the real world and placing iton to a flat plane such as a computer screen or a piece of paper. Although the earth is best represented by a spheroid, the earth is sometimes treated as a sphere. Coordinate systems enable geographic datasets to use common locations for integration. A geographic coordinate system gcs uses a threedimensional spherical surface to define locations on the earth. Understanding coordinate systems and projections for arcgis. The signs of x,y coordinates in a projected coordinate system. The map of massachusetts in unprojected decimal degrees of longitude and latitude note the proportion of the lines and the circle. Understanding map projections landing page for kartoweb.
The system has been in use, with little change, since the astronomer ptolemy used them in his first world atlas in a. Understanding coordinate reference systems, datums, and trans. This selfpaced, online training teaches the fundamental concepts of map projections, datums, and coordinate systems and demonstrates how to use them using esris arcgis. For instance, in geometry we use x horizontal and y vertical coordinates to define points on a twodimensional plane. A projection is the means by which you display the coordinate system and your data on a flat surface, such as a piece of paper or a digital screen. A guide to coordinate systems in great britain ordnance survey. The signs of x and ycoordinates in a projected coordinate system. Understanding coordinate systems and map projections. For example, there are a number of raster dataset file formats that use an associated world file to define coordinate and pixel dimensions for the upper left corner of the raster dataset. When you define the projection youre simply identifying the coordinate system that is used to place you datas coordinates in the correct location. Download the list of supported geographic and vertical coordinate systems.
Pdf on jan 1, 1994, melita kennedy and others published understanding map. National and local gridstwo things youre probably familiar withare projected coordinate systems. These show up as distortions of area, shape, direction, distance, and scale. Demonstrate an understanding that no matter how we project spherical data. The course format includes detailed information on how these concepts are applied to different regions of the pacific islands. First, most people best understand geography in a cartesian coordinate system on a flat surface. Things can get complicated when you delve into coordinate reference systems and map projections. Whether familiar with the science and mathematics involved with projecting geographical data or learning it for. This book introduces and illustrates geographic and projected coordinate systems and offers information on how they can be applied to data. Coordinate systems, projections, and transformations. Geographic coordinate systems are threedimensional grids, while projected systems use map projections to view the world in 2d. Geodesy, coordinate systems, objectives and map projections. Geodesy, coordinate systems, and map projections objectives introduce the main concepts of geodesy coordinate systems, datums, ellipsoids, and geoids describe map projections and coordinate systems we use in gis two key questions what is the shape of the.
Ellipsoidal coordinate systems reference a mathematically derived spheroidal or ellipsoidal volumetric surface. Reference systems of maps and geographic information systems of. In cartography, a map projection is a way to flatten a globes surface into a plane in order to make a map. The coordinate reference system of the paper is related with the dimensional mathematical object in that way.
Identifying the coordinate system typegeographic or projected. It is thanks to the coordinates that we can create overlays in a gis and perform analyses that incorporate data from more than one layer. Pcs gcs projection method select the appropriate projection system based on a region of interest correctly project data sets to a new spatial reference system when needed. Technically, there are two classes of coordinate reference systems. A gcs includes an angular unit of measure, a prime meridian, and a datum based on a spheroid a point is referenced by its longitude and latitude values. Coordinate systems,also known as map projections,are arbitrary designations for spatial data.
Understanding coordinate systems, datums and transformations in australia article pdf available january 2009 with 8,432 reads how we measure reads. Articulate the leader in rapid elearning and communications. Understanding and using projections in oasis montaj. Projected coordinate systems are based on a plane the spheroid projected onto a 2d surface and utilize linear units feet, meters, etc. The most critical issue in dealing with coordinate systems is knowing what the projection is and having the correct coordinate system information associated with a dataset.
Whether you treat the earth as a sphere or a spheroid, you must transform its threedimensional surface to create a flat map sheet. 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. What is the importance of map projection in geographic. Datums, coordinate systems, coordinate reference systems. Since planet earth isnt flat,some distortions in the data will inevitably occurduring that transformation process. The decision as to which map projection and coordinate reference system to use. Project the globe onto a 2d surface there are lots of. A map projection is the mathematical transformation of coordinates on one surface, in our case the ellipsoidal reference surface of the earth, to coordinates on the projection plane.
The difference is that wgs 84 is a geographic coordinate system, and utm is a projected coordinate system. Understanding map projections and coordinate systems. An introduction to mapping coordinate systems and the use of gnss datasets with. The latitude longitude coordinate system uses angular measurements to describe a position on the surface of the earth. The coordinates are often chosen such that one of the numbers represents a vertical position and two or three of the numbers represent a horizontal position.
From the perspective of a geographic software design three coordinate systems can potentially be addressed. Coordinate systems geographic coordinates latitude and longitude geocentric coordinates x, y, z mass centre of the earth cartesian coordinates datums horizontal and vertical references ellipsoid geoid mean sea level vertical elevation geoid undulation role of gravity map projections properties. A coordinate system is a reference system used to represent the locations of geographic features, imagery, and observations, such as global positioning system gps locations, within a. Understanding coordinate systems for arcgis projection terminology from the arcgis glossary. A guide to using the latitude longitude map coordinate. Making sure your gis data is in the right place on the map. Map projections explained a beginners guide youtube. Defines origin and orientation of the coordinate axes as well the sizeshape of earth a map a 2d representation of the 3d earth with eastingnorthing coordinates an overview of ellipses, datums, and projections the projection. This requires a systematic transformation of the latitudes and longitudes of locations from the surface of the globe into locations on a plane. Each differ either in the order of the coordinate tuple or in the direction of increasing values. Whenever you make a map,youre abstracting information about the real world,and placing it onto a flat plane,such as a computer screen or a piece of paper. Mariners and aviators have been the primary users of latitudelongitude in the past. This mathematical transformation is commonly referred to as a map projection.
Geographic coordinate systems are based on a spheroid and utilize angular units degrees. A tutorial on map projections and geographic coordinate systems. Understanding map projections, datums, and coordinate systems. Everything you need to know to work with coordinate systems and projecting. We will taker a closer look at the popular mercator projection and examine how the projection. Learn what a map projection is, why they are used and what impact they have on maps gis systems. Although the earth is best represented by a spheroid, the earth is sometimes treated as a sphere to make mathematical calculations easier. Demonstrate an understanding that no matter how we project spherical data 3d onto a plane 2d, there will be distortion.
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