02: GPS

Yesterday in the Great Smokies
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Announcements

  • 74% prefer that their phone have location services instead of their camera.
  • Tasks. Book your reservation now! 🔗
  • No private tours of the map library. Use reservation.
  • Lab. Make it to recitation to practice! 🔗
  • Pizza party open house: Our lab, Oct 9, 3 PM.

Maps & wanderlust

  • Imagining over the mountain.
  • Raisz 1950s landform map 🔗
  • National Weather Service 🔗
  • Task 2 🔗

Review

Powers earned 🐉

  • Create (and own) data.
  • Start consuming data:
    • CSV, GeoJSON, Shapefile, GeoTIFF, & KML (in this module).
  • Practice: visualize bigfoot sightings. Download data.

Pro Tip 💯

  • Most desktop apps use a right-click for various functions.
  • Get a mouse for your laptop
  • or discover the magic gesture.

LOCATE

Where are people?

Real-time tracking is ubiquitous.

How do you know where you are without electronics?

Reference mapping

Reference maps

  • A curated record of natural and human-made features.
  • Navigation primary purpose.
  • Shape & surface of Earth primary concern.
  • U.S. Geological Survey (USGS) topographic maps. 🏅✨

Reading USGS maps

  • Use this USGS topographic map viewer
  • Find your neighborhood.
  • Find a map that was published before you were born.
  • Find a map that was published before your parents were born.

Reading USGS maps

  • Explore Lexington West topographic maps from 1906–2022 via this QGIS project
  • Find the scale, north arrow, and lat, lon values on the map.

Slippy vs static maps

  • Slippy, aka dynamic, maps change as you pan and zoom.
  • Static maps do not change – they are meant to be printed at a fixed size.

We'll make static maps

  • Implications?
  • We need to know the map's scale and orientation.
  • We'll discover that these two properties are tied to a map's projection.

Map scale

How far is that?

  • How much is the map reduced from the real world?
  • Commonly expressed on the map as a scale bar and representative fraction.

Scale bar

  • Graphic scale using a printed measuring rule on the map.
  • Maintains accuracy when map is enlarged or reduced.

Representative fraction

  • Ratio of map distance to ground distance.
  • 1:10,000 (1/10,000) means 1 unit on the map equals 10,000 units on the ground.
  • Not accurate when map is enlarged or reduced.

Verbal scale

  • 1 in to 2,000 feet
  • Not accurate when map is enlarged or reduced.

Map orientation

Which way is up?

  • Which way is north?
  • Allows you to use a compass for navigation.

Compass bearings

  • Desired direction of travel is called a bearing.
  • Relative to north in degrees (0–360).
Task 2.1

Virtual geocache

Virtual geocache

  • A number of locations that you need to find
  • using distance and bearing.
  • Visit this page to start.

Nearest geocache

  • from ChemPhys is 448 feet at 169°.
  • Walk in that direction. "View" is the clue.
  • When close, another clue will help you identify the feature.
  • ☠️ Watch out for hazards ☠️

You'll want to use your phone

Tips

  • Cache clearly identifiable – if you follow clues.
  • Work in teams.
  • Walk slowly when close. Look around, up, down, etc.
  • Use compass app to help with bearing.

Submit answers to Canvas as a text entry

+1 point extra credit for each correct answer

TIME

Nothing teleports:
it takes time to move.

Walk for 20 minutes

  • at exactly 3 miles per hour.
  • Where would you be?
  • Dead reckoning.

What else moves?

Earth

  • moves 15° of longitude per hour.
  • Time zones roughly follow these divisions.

Your clock says 10 am

  • The sun is rising.
  • At the home port, the sun rose at 6 am.
  • Four hours difference = 60° west of home port.

1759

  • John Harrison's H4 chronometer.
  • Allowed accurate time at sea, thus accurate longitude.
  • Two short videos follow.

GPS

1970s

  • We make atomic clocks
  • that keep the best time measurements (like ever).

1995

  • These clocks are put in satellites
  • that broadcast their time and location to us
  • with global coverage.

Global positioning system (GPS)

  • US satellite-based navigation system.
  • Constellation of (at least 24) satellites.
  • One of many global navigation satellite systems (GNSS).

How?

  • Satellites broadcast their location and time.
  • Signals travel 186,000 miles per second.
  • Difference in time between satellite and receiver is used to calculate distance.
link

🤯

  • Miles to satellite =
  • time difference * 186,000 miles per second.
  • Four satellites needed to calculate 3D position.

Accurate?

  • You tell me.
  • Was much less accurate before 2000.

Selective Availability

Intentional degradation of signal until May 2000

2000s

  • iPhone and Street View
    • use GPS to geocode other data.
  • Enable Street View for this map.
  • In 2019 10+ million miles mapped with GPS.
  • And, now there's Dog View...

GPS

Is in everything!

Deliberate fitness tracking

🔗

unintentially maps military bases.

Surveillance

Privacy?

  • Your location is a commodity.
  • Surveillance capitalism.
  • Observations of you are sold to highest bidder.

Are you being tracked?

  • Do you mind if private companies log your location
  • and sells it?
  • Check your apps...

IKnowWhereYourCatLives.com

  • and where you do, too. 🔗
  • Experiment showing how location is shared.
  • Do you read the fine print?
A love letter to campus

Our collaboration

  • We made CSVs of 725+ places
  • that are meaningful to us.
  • View the interactive map.

Responsibilities

  • 1. Data must be formatted properly.
  • 2. Points must accurately represent locations.
  • Otherwise can't build map and it won't be meaningful.

Analysis

  • Where are the most popular places?
  • Dense cluster of points
  • show places that are meaningful to many people.

Heat map

  • Shows clusters as 'hot spots'
  • and identifies general patterns.

Voronoi polygons

  • Create polygon layer from points
  • where each polygon shows area closest to generating point.

Largest polygon

  • Fewest points nearby.
  • Most 'exotic' location.

Smallest polygon

  • Most locations nearby.
  • Most 'chosen' location.

Download your data

Lab 2

Happy Geom Society

  • Walk a polgon (or closed shape) on campus
  • rectangle, circle, or triangle.
  • Record the track with your phone's GPS.

Requirements

  • Read docs 🔗
  • Submit a KML
  • of a polygon that you walked.
  • 3-minute video 🔗

Open QGIS

  • To visualize KML path.
  • Download and install base maps 🔗
  • Submit a KML
  • video 🔗

Projections

Coordinate systems

  • One to define the shape of the earth Geographic
  • Another to define the shape of the earth on a flat plane Projected
  • Unit of measure
    • angular: degree
    • linear: meter or foot

Geographic coordinate systems

Shape of earth

  • Define sphere-like shape of earth
  • and measure with latitude and longitude.
  • Graticule
  • with angular unit of measure.

WGS 84

  • Coordinate system used by GPS.
  • 38.05°, -84.50°
  • Reference code is EPSG:4326

Projected coordinate systems

Earth flattened

  • Project sphere-like shape onto flat surface
  • using a plane, cone, or cylinder.
  • Makes a grid
  • with linear unit of measure.

Learn more

Distortion

  • When you project a sphere onto a plane you can maintain:
    • area (equal-area projections)
    • shape (conformal projections)
  • But not both on the same map.

🔍 Handle distortion

  • Primary goal: minimize distortion.
  • See how circles distort on different projections. 🔗
  • Find a suitable projection for map's scale and intent. 🔗

Practical advice

  • Let's focus on five projections.
    • Equirectangular
    • Mercator
    • Equal Earth
    • Albers equal-area
    • Local conformal

EPSG codes

  • European Petroleum Survey Group
  • makes 4–6 digit codes for coordinate systems.
  • Why are they concerned about map projections?
  • They have become the de facto standard – use their codes!

Equirectangular

  • EPSG: 4326
  • Lines of latitude and longitude make squares.
  • Default projection for data in WGS 84, i.e., GPS coordinates.
  • Distorts area and shape – don't use it!

Equal Earth

  • EPSG: 8857
  • Good projection for world maps.
  • Preserves area but distorts shape.

Mercator

  • EPSG: 3857
  • Lines of latitude and longitude are parallel.
  • Default projection for most web maps.
  • Preserves shape but distorts area.

Albers equal-area

  • EPSG: 102008
  • Good projection for North America.
  • Preserves area but distorts shape.

Local conformal

  • EPSG: 3089 (for Kentucky)
  • Tuned to small areas like states.
  • Minimizes distortion of shape and area.

Different state?

Why worry about projections?

  • It's complicated, but
  • when you pick the right one you can measure stuff
  • and cats sleep better.

Games

  • Geocaching.com 🔗
  • Geoguessr.com 🔗
  • Free, virtual cache (extra credit) 🔗

Summary

Reference maps

  • What is their primary purpose?
  • What two elements of a reference map do we look for?
  • What is a bearing?

GPS

  • What is required for GPS to work?
  • What are the privacy concerns using GPS?
  • What coordinate system does GPS use?

Projections

  • What is the goal of a map projection?
  • Name two types of distortion produced by a projection.
  • What five projections do we use?