GEOG181 Midterm Exam - PDF

GEOG181 MIDTERM  LOGISTICS Midterm will be held in-class during the first 75 minutes It will be 6 questions in total 1 Matching 5 short answer A total of 42 marks and worth 20% of your course grade Aids permitted: non-programmable calculator (no p...

GEOG181 MIDTERM  LOGISTICS Midterm will be held in-class during the first 75 minutes It will be 6 questions in total 1 Matching 5 short answer A total of 42 marks and worth 20% of your course grade Aids permitted: non-programmable calculator (no phones) Cover lectures up to October 21  KEY TOPICS Good map design Latitude/Longitude grid/angles Representation of the Earth’s surface (ellipsoids/geoids/datums) History of cartography Projection characteristics  SAMPLE QUESTION 1 At a latitude of 35º N what is the shortest distance between a point at a longitude of 80º E and 120º E. 111 cos Int Δ 1 longitude 91 km 40 3637 Shortest distance 3632km  SAMPLE QUESTION 2 If a projection is conical in shape and the apex of the cone corresponds to the north pole, we would call this projection… orientation pshawof projection surface Normal Conical How would we draw this projection?  SAMPLE QUESTION 3 What are essential elements for a map? What are things to keep in mind for making a good map? legend title north arrow scale audience citations data mapmakerdate use of white space  MAP PROJECTIONS AND DATUMS  OUTLINE Projection Methods Geographic versus Coordinate Systems Datums Source: otrmaps.files.wordpress.com 8 CYLINDRICAL MAP PROJECTIONS Projecting onto a cylinder  CYLINDRICAL PROJECTIONS  Cylinder wrapped around globe If ◦ tangent to globe along a great circle ◦ secant to globe along two small circles  normal orientation assumes cylinder tangent along the Equator ◦ meridians and parallels form rectangular grid  distortion increases with distance from standard lines  useful for projections of the world or regions with narrow extent in one direction, e.g. tropics, Chile 10  PATTERN OF DISTORTION: CYLINDRICAL distortion if mappingpeople US Geological Survey, National Atlaspublic domain) iitortion 11 http://www.nationalatlas.gov/articles/mapping/a_projections.html CYLINDRICAL PROJECTIONS minimaldistortion 12  EQUAL AREA PROJECTION Orthographic projection extreme distortion in polar regions not widely used since other equal area projections have less distortion of shapes I 13  EQUIDISTANT PROJECTION Also called plate caree parallels equally spaced along meridians N-S distances and distance along standard parallels are true to scale 14  SINUSOIDAL PROJECTION Start with equidistant projection --> scale all parallels so they are true to scale equal area projection distortion ↑ from intersection of Equator and central meridian 15  INTERRUPTED PROJECTIONS minimize distortion Goode Homolosine interrupted two ways 16  MERC ATOR PROJECTION  Conformal projection  adjust spacing of parallels so N-S distortion = E-W distortion at any point  loxodromes appear as samestretching straight lines issue with unequal area 17  GALL-PETERS PROJECTION Introduced in 1973 by Arno Peters Equal area projection Introduced to challenge distortions caused by the use of the Mercator projection issue with shape 18  MERCATOR AND GALL- PETERS PROJECTIONS COMPARED area shape 19  EQUAL EARTH PROJECTION extendslengthof meridians Preserves area – parallels arestraight Pseudocylindrical – More pleasing appearance than Gall Peters – B. Šavrič, T. Patterson, B. Jenny, 2018 – 20 21 SO, WHAT’S WRONG WITH THIS APPLE? 0 Africa is 14 times larger thangreenland Source: otrmaps.files.wordpress.com http://fuckyeahcartography.tumblr.com/post/27715397414 THE RELATIVE SIZE OF AFRICA 24 CONICAL MAP PROJECTIONS  CONIC PROJECTIONS cone tangent to globe along one small circle or secant to globe along two circles Tangent basic pattern A apex of cone on globe’s axis of rotation meridians are radial straight lines parallels are concentric circular arcs distortion increases with distance from standard line(s) secant useful for projections of mid-latitude regions, e.g. Canada, United States 26  PATTERN OF DISTORTION: CONICAL lessdistortion atequator Delmelle, Eric & Dezzani, Raymond. (2009). Overview, Classification and Selection of Map 27 Projections for Geospatial Applications. 10.4018/978-1-59140-995-3.ch012.  EQUIDISTANT CONIC PROJECTION Parallels equally spaced along meridians pole represented as circlular arc N-S distances and distances along standard line(s) are true to scale 28  LAMBERT CONFORMAL PROJECTION Adjust spacing of parallels so N-S scale = E-W scale at every point distortion becomes extreme south of Equator analogous to Mercator projection moredistortion 29  ALBERS EQUAL AREA PROJECTION Adjust spacing of parallels to maintain constant areal scale popular for representation of Canada 30 COMPROMISE PROJECTIONS 31  COMPROMISE PROJECTIONS gave up maintaing geometric equalities compromises factors toget a good projection Van der Grinten 1904 Used by the National Geographic Society for general world reference maps from 1922 - 1988 gives us niceshapeof the Earth even if area is distorted 32  COMPROMISE PROJECTIONS Robinson Replaced Van der Grinten 1988-1998 straight 33  COMPROMISE PROJECTIONS Winkel Tripel Replaced Robinson projection in 1998 34  Waterman Butterfly: Maintains shape, and minimizes other distortions. The perfect projection? http://www.watermanpolyhedron.com/worldmap.html  Dymaxion projection Buckminster Fuller – 1943 Earth projected onto a developable surface that is an icosahedron (20 faces) Converts globe into 20sided figure http://teczno.com/faumaxion-II/ COORDINATES & DATUMS  Geographic coordinates Divide world up into degrees, minutes, seconds of latitude and longitude can also be written as decimal degrees, or decimal fraction of whole d, m, s. 44° 57’ 19N”, -93° 6’ 29”W vs. 44.955482N, -93.108214W Gives unique location, but can be difficult to work with http://blog.geogarage.com/2010/03/tintin-and-location-by- geographic.html Length of one degree varies as you move around the planet  PLANE COORDINATES Cartesian co-ordinates: x,y Also known as projected coordinates Local co-ordinate system often used for field survey work important for GIS All countries use rectangular grid co-ordinates on local, large scale, maps easier to measure or calculate distances, areas, etc.  UNIVERSAL TRANSVERSE MERC ATOR PROJECTION (UTM) Normal Cylindrical Basis for Canadian topographic maps Used in many other countries around the world Composite projection: world divided into 6 degree longitudinal zones minimizes distortion foreach zone separate secant transverse Mercator projection for each zone centered on the central meridian of the zone ensures minimum distortion of geometric properties since all areas close to standard lines  UTM PROJECTION f 1  UTM GRID REFERENCES Civilian System Longitudinal zones numbered from 1 to 60 beginning at 180 degrees W, and moving east. 8 degree latitudinal zones (excluding the polar regions) labeled from C to X (omitting O and I) from south to north. Example: Kitchener-Waterloo in zone 17T Note: When working with UTM in a GIS O like QGIS, the northern or southern hemisphere of a zone will be indicated. YE For example 17N or 17S  UTM GRID REFERENCES Civilian System Each zone is divided into the northern and southern hemispheres. (i.e. 17N and 17S). The northern and southern hemisphere of each zone gets its own set of Cartesian coordinates To ensure Eastings and Northings are always positive, use false origin 500 km west of central meridian Equator is origin for northern hemisphere and is given a Northing of 10,000,000 m in southern hemisphere each zone has it's own artesian coordinates Universal Transverse Mercator Zones O http://students.ee.sun.ac.za/~riaanvdd/coordinate_systems.htm  UTM GRID 180 W 0E 180 E 84 N X T P N 0N J H C 80 S 1 17 60  UTM - WHY 80 O S AND 84 O N? “Each zone extends from 80°S latitude to 84°N latitude; the reason for the asymmetry is that 80°S just happens to fall very conveniently in the southern ocean, south of South America, Africa and Australia; but you have to go up to 84°N to reach a point north of Greenland” (Warner College of Natural Resources - Colorado State U) incorporating all majorland masses UTM FALSE ORIGIN LOC ATIONS EE are (Campbell 2001)  UTM GRID COORDINATES Eastings (longitude) To ensure Eastings and Northings always positive, central meridian is assigned value of 500,000 Northings (latitude) Measured relative to equator In N hemisphere, Equator is 0, in S hemisphere is given a Northing of 10,000,000 http://therucksack.tripod.com/MiBSAR/LandNav/UTM/UTMcoordinateDetail.jpg Easting 533,400 Northing 4,813,700  UTM PROJECTION REVIEW Composite Projection 60 zones of 6o longitude each, from 80o S to 84o N, numbered 1 to 60. Each longitudinal zone divided into 8o latitudinal zones lettered C to X omitting I and O. False origin created 500,000m west of central meridian on the equator (for northern hemisphere). Coordinates of any point can be specified by easting and northing coordinates. Example: EV1 building at approx. 537,000e 4,812,700n NTS topographic maps show UTM grid. important to be aware of Utm becuz widely used NORTH, NORTH, NORTH  three norths:  true north:  direction of north pole  meridians of longitude point to true north and south  grid north: North according to  based on rectangular UTM co- vitaminsThings ordinates  diverges from true north as move away from the central meridian, especially near poles  magnetic north:  direction sensed by compass  depend on Earth’s magnetic field at observer’s position  THE NORTH MAGNETIC POLE IS SPEEDING UP. Since the turn of the century, the speed at which the pole is moving has increased from about 9 km/yr to about 50 km/yr. (https://commons.wikimedia.org/w/index.php?curid=46888403)  DECLINATION DIAGRAM summarize relationships between three north points (at the centre of the map) Grid North * M True North a c Magnetic North Increasing 20’ annually a = magnetic declination at publication date c = convergence angle  True Grid DECLINATION Magnetic DIAGRAM  DECLINATION DIAGRAM Example: azimuth measured from true north is 35o what is azimuth from grid north and magnetic north? azimuths measured clockwise from north from grid north: 35o – 10o = 25o from magnetic north: 35o + 14o = 49o  DATUMS provides a frame of referencing for measuring location onthesurface ofEarth We have now discussed 2 coordinate systems… lat/long and UTM… but… we have not attached these coordinates to the model of the surface of the earth. Datums give us a reference… a starting point for measuring coordinates. They provide a system for anchoring an ellipsoid to the geoid and known locations on the earth’s surface. take ellipsoid and match to where we are on Earths surface  DATUMS For a datum you need: A starting point: An indication in the field (usually via a monument) of where the datum's initial point is located, along with measures of the latitude and longitude coordinates of this initial point. An axis: The azimuth of a line connecting the datum's initial point to a secondary point. This secondary point must also be identifiable in the field (once again, usually via a monument). A model of the Earth: The precise definition of the model of the Earth upon which the datum is based. Usually, if a is being used to represent the Earth, this is specified by the radius and flattening of the spheroid. The datum's separation: This value, which is usually (but not always) zero, indicates the vertical distance between the actual surface of the Earth and the surface of the datum's model of the Earth  RELATIONSHIP OF LAND SURFACE TO GEOID AND ELLIPSOID GPS (global positioning system) measures elevation relative to spheroid. Traditional surveying via leveling measures elevation relative to geoid. Land surface mean sea surface (geoid) Perpendicular Perpendicular Ellipsoid to Ellipsoid to Geoid (math model) (plumbline) Geoid (undulates due to gravity) Note also that elevation causes distances measured on ground to be greater than on the spheroid. Corrections may be applied.  DATUMS: ALL SURVEYING IS RELATIVE TO A SPECIFIC DATUM For the Geodesist a set of parameters defining a coordinate system, including: the spheroid (earth model) a point of origin (ties spheroid to earth) For the Local Surveyor a set of points whose precise location and /or elevation has been determined, which serve as reference points from which other point’s locations can be determined (horizontal datum) a surface to which elevations are referenced, usually ‘mean sea level’ (vertical datum) points usually marked with brass plates called survey markers or monuments whose identification codes and precise locations (usually in lat/long) are published.  ORIGINAL NORTH AMERIC AN DATUMS 1900 US Standard Datum first nationwide datum Clark 1866 spheroid origin Meades Ranch, Osborne County KS determined by visual triangulation approx. 2,500 points renamed North American Datum (NAD) in 1913 when adopted by Mexico and Canada NAD27 Clark 1866 spheroid Origin: Meades Ranch, Kansas visual triangulation 25,000 stations (250,000 by 1970) NAVD29 (North American Vertical Datum, 1929) provided elevation basis for most USGS 7.5 minute quads Used in OBM 39.2240867167°N 98.5421516778°W  NAD83 AND WGS84 NAD83 good for mapping North American coordinates satellite (since 1957) and laser distance data showed inaccuracy of NAD27 1971 National Academy of Sciences report recommended new datum used GRS80 ellipsoid (functionally equivalent to WGS84) origin: Mass-center of Earth 275,000 stations NAVD88 provides vertical datum points can differ 10 to 250m from NAD27, completed in 1986--but GPS more accurate! WGS 84 slobe basedsystem World Geodetic System Entire Earth surveyed using satellites – several updates In North America, almost identical to NAD83 (within 4m). System used for the globe and for GPS. CGVD2013 recently released for Canada NAD27 VS NAD83 About 215m difference Green – NAD83 Outline – NAD27  LOC AL BENCHMARKS Local government agencies will add their own benchmarks to densify the network  MAP SC ALE The nominal (principal) scale of a map is the ratio of the radius of the generating globe to the radius of the Earth OR: the ratio of distance on the map to distance on the earth. expressed as: verbal statement: 0 5 10 km 1 cm = 1 km representative fraction: 1 : 100,000 or 1/100,000 graphic scale  BUT! SC ALE IS NOT UNIFORM ACROSS SMALL SC ALE MAPS! Remember that scale varies dramatically across projections such as Mercator The published (or principal) scale of a map is only correct at the standard point or line(s) Distortion increases as you move away from the standard point or line(s). Distortion indicates a change in scale Variable scale bar: Can be used for certain projections (generally cylindrical) such as Mercator  SC ALE CONVERSIONS showsmore if you change the scale of a map from 1:25,000 to 1:50,000 have you enlarged or reduced area covered by the map? assuming the map sheet size stays the same: will the map show a larger or smaller area? will the map show more or less detail? what is the effect of this linear scale conversion on the areal scale of the map? what if you change the scale from 1:60,000 to 1:20,000?