Scale Factor - GIS and Mapping - Lecture Slides, Slides of Geochemistry

Download Scale Factor - GIS and Mapping - Lecture Slides and more Slides Geochemistry in PDF only on Docsity! Map projections Docsity.com The world is like an orange … Watch video (2.5 min) Docsity.com Literally projecting the globe onto a map … 3 of the earliest projections (by the ancient Greeks) [Gnomon = pagan sundial] Docsity.com Projection Terms a. Scale Factor (SF) • No map projection maintains correct scale throughout the map • The distortions increase as the distance from the central point of the projection increases. SF = scale at any location / divided by the 'principal scale' e.g. if actual scale = 1:2 million and principal scale = 1:1 million then SF at that point = 1/2million divided by 1/1million = 1/2 (0.5) Docsity.com Projection Terms a. Scale Factor (SF) For example, in any projection, where every line of latitude is equal in length (whereas the relative lengths on the globe are 1 at the equator, 0.5 at 60 latitude and 0 at the Poles), SF along lines of latitude are: at the equator SF = 1; at 60, SF =2; at 90, SF = ∞ The SF in the other direction (along meridians) may not be the same. 0 60 90 Docsity.com CONIC projections … are all ‘normal’ (e.g. Albers) They can be varied by : A: angle of the cone B: 1 or 2 standard parallels Docsity.com e. Distortion: compared to the graticule: Lines of latitude are 'parallel' and evenly spaced. Meridians converge at the poles, half at 60 degrees. All grid lines cross at right angles. Scale factor is 1 in all directions. ‘Great circles’ are straight lines e.g. meridians, equator, 'straight' flight lines Docsity.com Azimuthal equidistant map centred on St. John's, NF “AUSTRALIA — \ . a. . F ; % = oe <6 i f i S ~ a] ae 7 ria { S a aN) f fo r \ ie go t Treinaoeurate. AY p re’ ‘ LE ne : _ Cal ob 2000 soon 4000 =, = Mies faphy. Neeor iva of Newsantond 1's, Newfrundiand, CANADY Docsity.com Mercator’s Projection 1569 - conformal All ‘straight lines’ have constant compass bearings = Rhumb lines Docsity.com Lambert Equal-Area projection SF x SF (N-S, E-W) = 1 …. at any point e.g. equator 1,1 60N/S 0.5, 2 Docsity.com c. Distance Distances can be correct in one direction from a line, usually a standard line … or distances can be correct in all directions from a point. In these cases, the projection is termed equidistant (but only N-S) Plate Carrée projection Docsity.com Conic Cylindrical Planar (azimuthal) Sub-groups based on projection orientation (normal, transverse, oblique) Map projections – 3 major groups/techniques Docsity.com Pseudocylindrical (conventional) Projections • Can be called a 4th group of projections based on variations of the 3 main techniques. • attempts another trade-off of shape vs. area; in the normal equatorial aspect, they are defined by: straight horizontal parallels, not necessarily equidistant and arbitrary curves for meridians, equidistant along every parallel Sinusoidal projection Docsity.com How does a map show the positional relationship between two features, and their size and shape? Projection types/properties: • Equal-Area (equivalent) -correctly shows the size of a feature Conformal (orthomorphic) -correctly shows the shape of features (A map can not be both equal-area or conformal – it can only be one; or the other; or neither.) • Equidistant -correctly shows the distance between two features • Azimuthal (True Direction) -correctly shows the direction between two features Docsity.com Canada Albers Equal Area Conic: Central Meridian: -96 Latitude Of Origin: 40 First Standard Parallel: 50 Second Standard Parallel: 70 Docsity.com Arc Map example MAPSIO1 - ArcMap ile tdit Vew Insert selection Lools Wincow HsIp QB BAO 6 Si s]|\e 8 a QQuN MOS OROMa? 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Da Predefined B71 Fraser Besin Fh & Fraser Watersheds Legend oa Shee 2 outon = Bae | war 4.3 mayne I) P33 — 1s Ba Bivens dtd To Favoriler = sean. con 33 te ae [= Hemave tem ravoutes| 4 Indien Receves 10D ColumbiaRiver nines ta 2) Fever be MesingorRver 137 Nechae ner a 2] Star tier 147 West Roe Glecvate) ter 7 Quel ve Catogramer: Kim MacLean Darel4 Dooorreer 2012, Cylindrical Projections 16th century -> Best for equatorial areas and used for world (historical) maps -fill a rectangular shape Mercator (16th century) Transverse Mercator Docsity.com 4. Conventional (pseudo-cylindrical) Projections -19th century (and 20th) These are geometrically constructed. The parallels are generally equally spaced but are made more proportional to their real length to minimize distortion. Mollweide Docsity.com Conventional projections -Generally show the whole world with least overall distortion (and are equal-area) -19th century (and 20th) -E.g. Mollweide’s homolographic Tissot’s Indicatrix of distortion Docsity.com Robinson projection – adopted by National Geographic in 1988 Poles drawn as lines to create better shapes Docsity.com Bit Cre Cee Cissy Tne GIy s ANOLON SII POLAR REGIONS onmental and Social Sustainability? Sie a ; ~ i é& 4 Edited by Michael Lack, 1 Patrick T. Maher and Emma J. SP¥S csity com One more projection .... The butterfly map * WATERMAN’S ¥ ATLANTIC VIEW WORLD MAP Docsity.com  one last one ... the Moocator (projection humour) Docsity.com