# Chapter Two - Navigating Our World: Geodesy, Datums, and Coordinate Systems

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### Chapter Goals

 Define and explain classic geodesyDefine and explain modern geodesyDefine and explain GNSSDefine topographic surfaceDefine geoidExplain what a geoid is a model of how the model is madeExplain why geoids are used in GIS and CartographyDefine ellipsoidDefine spheroid (ellipsoid of revolution)Define reference ellipsoid, global reference ellipsoid, local reference ellipsoidExplain when and why we use ellipsoidsExplain when and why we use spheroidsDefine and explain Cartesian Coordinate SystemsDefine geodetic datumExplain how geodetic datums are madeDefine benchmark and control pointsExplain the similarities and difference between benchmarks and control pointsDefine and explain horizontal and vertical datumsDefine orthometric heightDefine ellipsoid height Define geoid separationExplain when we use orthometric height, ellipsoid height, and geoid separationDefine and explain datum shifts, both major and minorDefine Earth-centered, Earth-fixed Coordinate SystemsDefine and explain geographic gridExplain where a geographic grid is drawnThoroughly explain geographic coordinate systems (GCS) including the parts it's made up of, why it's used, and how it differs from a geographic gridDefine projected coordinate systems (PCS)Explain the advantages of PCS'sExplain the disadvantages of PCS's Define and explain distortion, naming the six kinds of distortionDefine and explain developable surfaceName the three major developable surfacesDefine and explain projection aspectName the three major projection aspectsDefine and explain projection methodExplain the difference between a projection method and a PCSDefine and explain the State Plane Coordinate SystemDefine and explain the Universal Transverse Mercator (UTM) systemDefine map scale