Digital Mapping
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Week5lecture1finishupflatearthandprojections1.pptxComing up…
Today – Flat Earth, Projections, Projections Lab
Tuesday – Final Lab before midterm (go over in detail – your answers here will be used on the first part of the exam)
Tuesday 19th night release review
Thursday 21st review – release take home exam (focused on lab portion of exam – technical tasks )
Tuesday 26th – Exam Part I Creatively Use answers from take home exam in class – for example you will do a mini-lab exercise on Google Street View. When you come into class you will answer questions related to the course about it. You will be able to use your phone to access your take home exam (or print it out)
Thursday 28th – More traditional short answer exam based on lecture (no resources for help)
Last Time
Went over Lab
Coordinate Systems
Earth is a real place
It’s bumped and bruised
We create a model based on the earth’s surface at a given location
NAD 1983 when mapping North America
Create an ellipsoid to transform real world into mathematical model
Create model and draw lat and lon lines
Flat earth – the start of legitimacy
Projections
Still have to get the globe on a 2-D surface
Distortion!!!
Making decisions as a cartographer about accuracy and appearance
ALL MAPS ARE LIES!
“To avoid hiding critical information in a fog of detail, the map must offer a selective, incomplete view of reality. There's no escape from the cartographic paradox: to present a useful and truthful picture, an accurate map must tell white lies.” (Monmonier 1992)
Projection
The method by which our estimation of the shape of the earth is assigned to a two-dimensional surface
A mathematical transformation – different types – cylinder, cone, or flat surface
What’s up with the geometry????? You are literally projecting the globe onto a surface
Lamp demo
7
Distortion
Properties that can be preserved or distorted:
Shape (conformal map)
Distance (between one single point and any other - equidistant)
Area (Equal Area)
Direction (azimuths for all directions)
The larger the extent, the greater potential for distortion
Sacrifice…
Shape: scale at any point on the map is the same in any direction
Skip scale slides if no time
9
Methods of projection, or projection families
North America Albers Equal Area Conic Preserves area at middle latitudes Accurate but only in certain areas
Mercator Projection Preserves Shape Distorts Size at low and high lattitudes
North Pole Azimuthal Equidistant It has the useful properties that all points on the map are at proportionately correct distances from the center point GOOD FOR DISTANCE! SIZE, SHAPE, AND DIRECTION DISTORTED
Flat Earth Society Adopts this Map
On Exam: A Map is a representation of Space. Use projections/coordinate systems to make an argument for this statement.
Dude – couldn’t they do that with space photos???
Confirmation Bias and Cherry Picking Science
“I don’t know… I’m crazy bro”
“You’re on a ball – go nowhere – stay where you are”
If space travel was faked because of economic/political gain – what is this?
Earth is centered at north pole and bounded along it’s perimeter by a wall of ice.
Conspiracy Theories
The hidden truth and feeling smart/unique
Transcendent knowledge/Cult Status/belonging
Need for order/security/explanation
(Maps/Lat/Lon provide this)
The sun, moon, and stars are only a few hundred miles away
Touch Lines
Tangent vs Secant
Lines of accuracy…
Tissot’s Indicatrix
Plate carrée or geographic projection
North America Lambert Conformal Conic
Preserves distance along meridians
Preserves shape
Preserves distance and direction from center
Polar Azimuthal Equidistant
Sinusoidal
Preserves area
Mercator
Preserves shape (except at poles)
Preserves everything (in 3-D)
Orthographic (Earth from space)
Azimuthal Equidistant
Scale is true at the center point
Distance is preserved on any line from the center point
Gnomonic Projection
Any line drawn between two points is a great circle
Scale is true only at the center point
No other properties preserved
Peters
Outline
Fundamentals
Datums, degrees, and graticules
Projections
Strategies for picking the projection (the lab)
Considerations when choosing a projection
Purpose
Reference, navigation, surveying, analysis
Audience
General, specialist
Extent
Distance, areal coverage, relative distances
Location
Polar, tropical, mid latitude
UTM
Strategy: works well for most places with large north-south extent
Reasonably good preservation of shape, distance, area, and direction for almost anywhere within a zone
60 Zones – unique coordinate system and central meridian
State Plane Systems
State Plane
Socially agreed upon projection for places in the United States (Government, real estate, etc)
Use if area you are mapping is entirely within one area.
Better for smaller areas
Only good for United States
How do projections change the way maps look?
Cylindrical Projections
Projection surface is a rectangle
Scale is true along a tangent line or secant lines
Mercator
Mercator
Standard parallel (tangent case) at the Equator
Useful for navigation and mapping equatorial regions
Gerardus Mercator, Flemish/German/who knows 1569 map
35
Conic Projections
Projection surface is fan-shaped
Scale is true along standard parallel(s)
Used for areas with east-west extent
Lambert, Albers
Azimuthal Projections
Projection surface is circular
Scale is true at the central point (tangent case) or along a circle (secant case)
Often used to map polar regions
Quiz
What is the difference between a coordinate system and a projection
