A projected coordinate system pcs is a gcs that has been flattened using a map projection. Some basic ideas about the mathematics of map projections. It is possible to add a utm grid to a map that is only marked with. This type of figure is termed an oblate ellipsoid or spheroid, and is the threedimensional shape. A projected coordinate system is defined on a flat, twodimensional surface. There are many different coordinate systems, based on a variety of geodetic datums, projections, and units in use geographic coordinate systems no projection. These show up as distortions of area, shape, direction, distance, and scale. When we use the term map projection, were referring to the relationship between the rows and columns of data in the 3d grid to the latitudelongitude of the earth. Map projections usually are classified by the projection surface used, such as conic, cylindrical, and planar. Common geographic coordinate systems are wgs 1984 and nad 1983.
The process of converting a threedimensional space to a twodimensional map is called projection. 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. In gis, there are many types of coordinate systems, of which the two most used are geographic 3d and projected 2d. A map projection systematically projects locations from the surface of a spheroid to representative positions on a flat surface using. D h maling a revised and expanded new edition of the definitive english work on map projections. There are several ways to refer to a coordinate system. The employed plane coordinate system is either projected or geographic. We introduce the mapping from a left riemann manifold to a right one specified as conformal, equiaerial and equidistant, perspective and. The earth has a circumference of around 24,900 miles, but is around 27 miles wider than it is tall. This powerpoint is available at gis linkspresentations understanding coordinate systems for arcgis 2. A projected coordinate system is always based on a geographic coordinate system that is based on a sphere or spheroid in a projected coordinate system. This projection is based on the mathematics of a cone intersecting a sphere.
A geographic coordinate system gcs uses a grid on the surface of a 3d globe the technical term for this grid is graticule. Map projections and coordinate systems clarke major. Coordinate systems, projections, and transformations. Spatial data has coordinate systems, geographic coordinate systems, or projected coordinate systems defined. D surface of the earth and its features are transformed onto a flat plane for the. Understanding projections and coordinate systems important knowledge to have, especially if you deal with many different sets of data that come from different sources. Coordinate systems enable geographic datasets to use common locations for integration. With a smallscale map, your choice of map projection determines the overall appearance of the map. The major online street mapping services tiling systems display most of the world at. Projection parameters to define the coordinate system completely, it is not sufficient simply to name the. Dana, department of geography, the university of texas at austin, and were developed as part of the geographers craft project at the university of texas at austin. Coordinate systems, map projections, and geographic datum. Presentation objectives understand basic concepts on coordinate systems for the gis user.
Lecture 2 map projections and gis coordinate systems. The circumference of the earth is about 0th smaller around the poles. A projected coordinate system is always based on a geographic coordinate system that is based on a sphere or spheroid. Projected coordinate systems are derived from map projections and geographic coordinate systems from latitude and longitude degrees. Usgs puts both latlon and utm coordinates on all of their large scale maps.
Understanding map projections, datums, and coordinate systems. This is changing somewhat as more data are collected by gps. For instance, in geometry we use x horizontal and y vertical coordinates to define points on a twodimensional plane. Pdf reference surfaces, coordinate systems and projections are the prerequisites for the geospatial analysis of planetary surfaces. Conceptual summary of projections aa coo d ate syste sn coordinate systems xy coordinatesderived via projection from latlong t iti 2 dfl t lines of latitude and longituderepresent position on 2d flat map surface spheroid. Projections and coordinate systems are a complicated topic in gis, but they form the basis for how a gis can store, analyze, and display spatial data. Understanding coordinate systems and projections for arcgis 1. Your organization mandates using a particular projected coordinate system for all maps. For example, with some projections, lines of latitude and longitude will appear curved. The revisions take into account the huge advances in geometrical geodesy which have occurred since the early. This selfpaced, online training teaches the fundamental concepts of map projections, datums, and coordinate systems and demonstrates how to use them using esris arcgis. Geographic information systems stack exchange is a question and answer site for cartographers, geographers and gis professionals. Arcmap will reproject all layers that have coordinate systems that arent the same as the data frames.
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. A practical guide to coordinate reference systems, datums and map projections. The course format includes detailed information on how these concepts are applied to different regions of the pacific islands. Maps are flat, so your map must have a pcs in order to know how to draw. In largescale maps, cartesian coordinates normally have a simple relation to eastings and. Gis data differs from other data types, primarily because it contains geographic coordinates describing the location of the data on the earth.
Your data must have a gcs before it knows where it is on earth. A datum transformation is a method that converts data between two geographic coordinate systems. Coordinate systems and map projections 2nd edition. On larger scale maps the choice of coordinate system is often determined by the coordinate references that have been supplied by the map maker. Gis positional data are primarily printed maps which have been digitized. Projections and coordinate system linkedin slideshare.
Learn about geographic coordinate systems and map projections and how to work with them in arcgis pro. We introduce the mapping from a left riemann manifold to a right one specified as conformal, equiaerial and equidistant, perspective and geodetic. Many other map makers only provide latlon references. Within or on top of the projection is a coordinate system containing the x and y location values, which incorporates the ellipsoid shape of the earth, datum known base values, and units e. A datum uses latitude and longitude or geographic coordinate systems to define the locations of points on the surface of a spheroid. Coordinate systems frameworks used to determine position on the surface of the earth. I set the projection of arcmap dataframe to projected coordinate system web mercator and changed the display values from meters to decimal degrees. Coordinate systems and map projections, second edition. The earth exists in threedimensions but, other than globes, most representations of the earth, such as maps, are two dimensional.
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. Objectives coordinate systems and map projections for gis. The earth is a spheroid it is round like a ball or sphere but flattened by slightly by the centrifugal force of rotation. Geodesy, map projections and coordinate systems gis in water resources, fall 2015 besides this synopsis, please read the overview of georeferencing and coordinate systems in the arcgis resource center.
Commonly used projections and coordinate systems in bc are utm and bc albers. Projections and coordinate systems may seem complex and arcane to you, but as you become more familiar with gis and gis datasets, you will become more capable of handling different coordinate systems and projections. Because maps are flat, some of the simplest projections are made onto geometric shapes that can be flattened without stretching their surfaces. Ellipsoidal coordinate systems reference a mathematically derived spheroidal or ellipsoidal volumetric surface. Introduction to coordinate systems and projections. Unlike a geographic coordinate system, a projected coordinate system has constant lengths, angles, and areas across the two dimensions. If layers in a map have different coordinate systems defined from those of the map or local scene itself, a transformation between the coordinate systems might be necessary to ensure data lines up correctly. The appearance, classification and naming of map projections. Though it displays latlon values, i think it is projected coordinate system. A coordinate system is used to translate locations on the surface of the earth to an image on a flat surface, like your computer screen.
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 common geographic framework. The figures on this page are the intellectual property of peter h. Geographic coordinates, latitude and longitude, are in fact not considered projected. Map projections are the means by which data about the 3. Projecting your data is optional, but projecting your map is not. The figure of the earth and the reference surfaces used in surveying and mapping. The process of projection involves distorition of area, distance, shape, and angles.
The mercator projection is a cylindrical map projection presented by flemish geographer and. Modern national mapping systems typically employ a transverse mercator or close variant for. Map projections cartographic information systems erik. Projections transformation of curved earth to a flat map. What it wont do is the geographicdatum transformation part if. Just as all maps have a map scale, all maps have locations, too. Spheroid or ellipsoid based systems, local systems.
Coordinate systems and map projections ebook, 1992. Projected coordinate systems, map projections, parameters, and linear units of measure current as of arcgis version 9. Pdf map projections in planetary cartography researchgate. 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. Buy coordinate systems and map projections, second edition on free shipping on qualified orders coordinate systems and map projections, second edition. Projections and coordinate systems using corpscon, the projector.
Some common examples are cones, cylinders, and planes. The earth exists in threedimensions but, other than globes, most representations of the earth are two dimensional. Map projections and coordinate systems features on a map refer to the actual locations of the objects they represent in the real world. Presented by john schaeffer juniper gis services, inc. Understanding coordinate systems and projections for arcgis. For remote sensing, gis and surveying has become a key book for many students and professionals around the world. Extension in arcview, and project in arcinfo marylands stateplane coordinate system is based on a lambert conformal conic projection.
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