UBC$Department$of$Geography$ GEOB$370$–Advanced…blogs.ubc.ca/advancedgis/files/2017/11/AlvarezLeon_UBC_Geo... · UBC$Department$of$Geography$ GEOB$370$–Advanced$Issues$in$GI$Science

UBC Department of Geography GEOB 370 – Advanced Issues in GI Science

Prof. Brian Klinkenberg

Guest Lecturer: Dr. Luis F. Alvarez León

University of Southern California November 21st, 2017

Georeferencing

Outline

1. Principles of Georeferencing 2. Commonly Used Systems 3. Conversions 4. Recap/Discussion

ObjecOves

• Understand how various georeferencing systems work, and conversions between them

•  Learn how posiGoning is done by measuring and modeling the Earth’s surface

• Understand map projecGons, and key examples

• Know the principles and applicaGons of GPS

Objec,ves Keywords Principles of

Georeferencing Commonly Used Systems Conversions Recap

ObjecOves

•  Think criGcally about how georeferencing works, what it is used for, and how it impacts the human and natural world:

How does georeferencing intersect with broader social, poli5cal, technological dynamics? How can thinking cri5cally about georeferencing, and GIS tools more generally, can improve our world?



Keywords

•  UTM (Universal Transverse Mercator) •  ProjecGon parameters:

‒  Surface orientaGon [normal, transverse]

‒  Form [plane, conic, cylindrical] ‒  Contact [tangenGal, secant]

•  Geoid

•  Datum (NAD27, NAD83) •  Ellipsoid (Ellipse) •  Cadastre •  WGS84 vs GRS80 •  A definiGon of metric



1. Principles of Georeferencing

• At its core: georeferencing is when we assign a locaGon to a parGcular informaGon point •  Simple idea; execuGon can get complicated. Deeply interconnected with how we experience and shape the world •  Three key requirements

1)  Unique -‐ only one locaGon for each georeference (area/context -‐specific, e.g. London, Ontario vs. London, England)

2)  Shared meaning -‐ within a large enough group of users 3)  Stable -‐ Persistent over Gme



• Georeference systems can be based on: ‒ Names (e.g. street names)

Easy to communicate, context-‐specific, difficult to translate and extend ‒ Measurements -‐ Called metric georeferences (e.g. coordinate systems)

PotenGal for ‘unlimited’ accuracy, can calculate distances, are less context-‐specific

•  They are crucial to navigaGon, communicaGon, logisGcs, etc. •  They also enable legibility & control by the state (James C. Scoe)



2. Commonly Used Systems

2.1. Place-‐names and Points-‐of-‐Interest (POI)

• Although endowed with meaning and history, these can vary • Only some place-‐names are officially recognized by gov. agencies. Many more locally recognized. Arbitrary, and limits communicaGon • Not always stable over Gme (names can be lost, change) • Geoweb is creaGng new alternaGves through VGI, Wikimapia, etc.



Pretoria, South Africa Image: AFP

Sea to Sky Highway, Squamish, BC Image: CBC

2.2. Postal Addresses and Postal Codes

• System created to deliver mail • Assumes that:

‒ Every dwelling is mail desGnaGon (many excluded) ‒ Dwellings located along paths, numbered sequenGally (cf. Japan, etc.) ‒ Name uniqueness within a scale (local areas < regions < countries)

• Does not work for natural features • Can be convenient for summarizing data about people/places



Image: Claritas

Image: DHL

2.3. IP Addresses

• Each Internet-‐connected device has an Internet Protocol (IP) address •  IP addresses are assigned to Internet-‐Service Providers and organizaGons -‐> posiGonal uncertainty. Increasingly accurate •  IP addresses can be converted to geographic coordinates • GeolocaGon of IP addresses revoluGonized the Internet in 2000s • Use and misuse has widespread privacy and security implicaGons



Image: Fusion

2.4. Linear Referencing Systems

• LocaGon idenGfied within a network by measuring the distance from a point of reference along a path • More reliable than street addresses; widely used in transportaGon infrastructure (mile markers) • Downsides: - Not robust across all applicaGons - Oken has to be converted to other systems (lat / long) - Long distances between intersecGons (rural areas) and irregular networks (mulGple, self-‐intersecGons, etc.) hamper pracGcal use



Image: West Maui Cycles

Image: Boulder Daily Camera

2.5. Cadasters

• Map of ownership created by subdivision. For taxaGon and public record of ownership (e.g. Domesday Book, 1086) • Unique idenGfier for each parcel. RelaGvely persistent. Mostly local government users • U.S. Public Land Survey System (PLSS) : 6 mi. X 6 mi. blocks framed by principal parallel/meridians ‒ Grid offset to accommodate Earth’s curvature; has some measurement errors

‒ Started 1784, took almost a century. Tied to geopoliGcal (war debt) and expansionary drive of U.S. (Western seelement)



Image: Jim Riesterer, Idaho State University

Image: Paden Cash, RPLS Today

Image: Nasa Earth Observatory

“The result [of the U.S. Public Land Survey] was an 'authored landscape’ […]” . Monmonier (1995, p. 114)

2.6. LaGtude and Longitude

• Very powerful, comprehensive georeferencing system • “Geographic” coordinate system: based on Earth’s rotaGon around center of mass • PotenGal for very accurate posiGonal measurement, distance between locaGons, and support for spaGal analysis






•  [φ] Lines of la,tude (parallels): Slices parallel to the Equator

•  180 degrees of laGtude 90S(-‐), 90N (+)

•  [λ] Lines of longitude (meridians): Slices parallel to the rotaGonal axis & perpendicular to Equator. Prime Meridian: Greenwich, UK

•  360 degrees of longitude 180 W(-‐), 180 E (+)

•  Distances between meridians shrinks as they converge in North and South poles




•  Geoid: surface of equal gravity formed by oceans at rest, imaginary extension under the conGnents

•  Ellipsoid: Three dimensional figure obtained by rotaGng an ellipse on its minor axis

•  Earth’s rotaGon on its axis flaeens its shape

•  Flaeening: f = (a-‐b)/a (close to 1 in 300)

Image: Steven Dutch, University of Wisconsin -‐ Green Bay




•  What ellipsoid fits best? -‐ Aker centuries of research, ICBMs led to a soluGon

•  WGS84 – World GeodeGc System of 1984 -‐ Used by GPS

•  GeodeGc datum: Unified network of surface measurements

•  NAD83 – North American Datum of 1983 (Earth Centered ref.) -‐ Closely matches WGS82 -‐ Basis of coordinates of all horizontal posiGons for Canada and the US -‐ Updates NAD27 (1927, fixed staGon ref.) – Differences can be up to 100m Image: Breaking Defense

2.7. ProjecGons and Coordinates

• ProjecGon entails flaeening a three dimensional object. Necessary to work with maps on various media (paper, photography, etc)

•  Transform locaGons from geographic coordinates (φ, λ) to Cartesian coordinates (x, y). Each projecGon has a different funcGon

• GI convenGon: Y axis = North, X axis = East

• All projecGons introduce some distorGons, especially for large areas. To work in GIS, it is important to know the projecGon and datum of each dataset





Mercator ProjecOon with Tissot Indicatrix Image: Vox

Mercator: Cylindrical, conformal Line of contact: The Equator or two laGtudes symmetrical around the equator


While projecGons introduce distorGon, they can preserve one of two key properGes:

1)  Conformal property – Shapes are preserved (scales on x and y are equal)

2)  Equal area property – ProporGons of areas in the map are the same

as those on the Earth




According to the physical model of how their flat surface relates to Earth’s curved surface, there are three major projecGon classes:

1)  Cylindrical 2) Azimuthal, or planar 3) Conic



•  Good for comparing laGtudes •  Unsuitable for world maps

•  Good for finding direcGons using central point as reference

•  Good for regional, hemispheric maps •  Unsuitable for world maps

4.7. Common projecGons 1)  Plate Carreé, or Cylindrical Equidistant 2)  Universal Transverse Mercator 3)  Lambert Conformal Conic



Plate Carreé, or Cylindrical Equidistant (cylindrical) – Assigns lat long to x, y – Regular grid – DistorGon of all properGes away from Equator (line of contact) – Used for small areas, or simple world portrayals



Plate Carreé ProjecOon with Tissot Indicatrix Image: Eric Gaba

Universal Transverse Mercator (cylindrical, transverse, lines of contact: central meridians and Equator) – Not a single projecGon – 60 zones of 6 degrees, each with a central meridian – Minimized distorGon within each strip, increases away from central meridians – Military applicaGons



Image: NaOonal GeospaOal Intelligence Agency

Lambert Conformal Conic (secant) – Based on two standard parallels – LaGtude spacing increases beyond them Lines of contact: standard parallel(s) – Used for regions with East-‐West orientaGon, in middle N or S laGtudes – LaGtude range should not exceed under 35 degrees



Image: Strebe

2.8. GPS

•  Developed by U.S. Department of Defense •  Part of a revoluGon in posiGoning with GLONASS (Russia) and Beidou (China) • Widespread use with enabled devices (phones, etc.) •  24-‐plus satellites orbit Earth every 12 hours and send radio signals •  Receiver makes calculaGons from signals, satellite posiGons and velocity of light •  Can calculate laGtude, longitude (three satellites), and elevaGon (four satellites)



Image: NaOonal Geographic

3. Conversions

• GI Systems are very useful for converGng between projecGons and coordinate systems • However, conversions between place-‐names and geographic coordinates are more problemaGc • Geocoding: Converts streets addresses to coordinates. EssenGal for many GIS uses • Place name databases have become vitally important in web environments (people search by place names)



4. Recap/Discussion

How do georeferencing systems shape how we can know, navigate, and impact the world? Consider: Who? , what?, when?, why?



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UBC$Department$of$Geography$ GEOB$370$–Advanced…blogs.ubc.ca/advancedgis/files/2017/11/AlvarezLeon_UBC_Geo... · UBC$Department$of$Geography$ GEOB$370$–Advanced$Issues$in$GI$Science