GEOG 370 1st Edition Lecture 3 Outline of Last Lecture I. Map projections: from a round earth to a flat mapa. Background: from a round earth to a flat mapb. Map projections: the basicsII. Map projection mechanicsa. Classb. CaseOutline of Current Lecture II. Map projection mechanicsa. Aspectb. CenteringIII. Map projection distortionsCurrent Lecture- Quiz 1o Distance between lines of longitude remains constant at every line of latitude (true or false)o Line depicting shortest distance between two points (multiple choice)- Map projection mechanics o Guidelines for matching classes with regions: Use a cylindrical projection with equatorial regions Conic for mid-latitudes (like the U.S.) Planar for polar regionso Guidelines for matching cases with map extents Tangent cylindrical and conic projections or secant planar projections, place single standard line in center For secant (cylindrical conic) place the pair of standard lines 1/3, 1/3, 1/3o Aspect: the orientation of the developable surface to the reference globe Impacts the position of the standard lines, and therefore the pattern of distortion across the map Aspects of developable surfaces (3):- Normal: a map projection with a developable surface that is oriented according to the earth’s axis of rotation  These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.o Note: descriptions of class and case above assume normality a normal aspect results in standard parallels, or standard lines that run along parallelso The standard point is at the north or south pole for a normal tangent planar projection - Transverse: a map projection with a developable surface that is oriented 90 degrees from the axis of rotation o A transverse aspect results in standard meridians, or standard lines that run along meridians (tangent cylindricalprojections only)o Example: UTM (universal transverse Mercator coordinate system) A system of 6 degrees longitude zones in a secant transverse Mercator projection Has 60 in total SF ≈ 1 everywhere in the zone - Oblique: a map projection with a developable surface that is oriented at an angle from the axis of rotation that is neither normal nor transverseo Used to show the great circle route between two locations as a straight line o Used to show perspective, or howthe earth wouldlook from a specificpoint in the sameatmosphere/fromspace o Use of an obliqueperspective for aesthetic purposes  Aesthetically pleasing, but not really for location or spatial needs Image below will probably be exam question - Guidelinesfor matching aspect with mapped phenomena (3):o Apply a normal aspect for geographic features that are oriented primarily east-west (i.e., that are best depicted with a landscape layout) Primarily for cylindrical and conic projectionso Apply a transverse aspect for geographic features that are oriented primarily north-south (i.e., that are best depicted with a portrait layout) Particularly for cylindrical projections o Apply an oblique aspect when you are emphasizing the relationship between two locations or a particular perspective on a single location o Centering Centering: the middle point and overall extent of your map- Put the region of interest in the center and make it as large as possible on the map page- Components of centering (3):o Central coordinate: the coordinate, geographic or otherwise, that is at the center of the map projection Described as the central meridian for normal map projections Either at standard line/point (tangent) or equidistant tostandard lines (secant) Centering is a second reason why Mercator is used for web mapping services- Total extent: the geographic area included in the map after cropping the projectiono A map does not need to show the entire worldo Crop areas with severe distortiono The aspect ratio, or the relationship between the horizontal and vertical axes of your map page, should match the general aspect ratio of the represented geographic phenomena- Interruption: slicing the developable surface to allow for multiple projection errorso Produces multiple lobes that are only partially connected in the resulting mapo The standard lines and central meridians are specific to each lobe - Map projection distortionso Types of distortions Distortion: the alteration of the shapes, sizes, directions and/or relative distances of a 3D reference globe when projected onto a 2D developable surface- Characterize a map projection by the properties that are preserved- All projections impose some kind of distortion Tissot’s Indicatrix: a method for graphically representing the distortions form standard lines o Types of projections based on the properties that are preserved (5): Conformal: a map projection that preserves angular relationships at infinitely small points- Often described imperfectly as the preservation of shape, but conformal maps do not preserve shape Equivalent: a map projection that preserves areas- Also: equal-area- Often used for thematic mapping when the size/area of symbols isimportant to map interactiono Particularly choropleth maps, but also isoline and dot density Cartographic controversy: equivalent projections have been proposed as a more socially just representation of the world  Equidistant: a map projection that preserves distance from either one point (planar) or two points (cylindrical and conic) on the map to any other points on the map- All maps are equidistant along standard lines (i.e., SF=1) Azimuthal: a map projection that preserves the direction from a single point, with all straight lines drawn form the center representing a great circle route- All azimuthal maps projections are planar- Azimuthal projections preserve angles from the standard point across the entire globe- Despite azimuth name, straight lines are not rhumb lines - Straight lines form the stand point are great circles Compromise: a map projections that preserves no map property perfectly, but maintains shape, area, direction and distance reasonably