02: GPS
Yesterday in the Great Smokies
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GEO 109: Digital Mapping
Review
Powers earned 🐉
Create (and own) data.
Start consuming data:
CSV, GeoJSON, Shapefile, GeoTIFF, & KML (in this module).
Practice: visualize bigfoot
sightings
. Download
data
.
Tip 💯
Most desktop apps use a right-click for various functions.
Get a mouse for your laptop
or discover the magic gesture.
Extra Pro Tip 💯
Understand what needs to be submitted for evaluation.
Don't know what to submit?
Ask us.
Before the assignment is due.
LOCATE
Where are people?
In cars?
🔗
In trains?
🔗
In boats?
🔗
In airplanes?
🔗
Real-time tracking is ubiquitous.
How do you know where you are without electronics?
Reference mapping
Reference maps
A detailed record of natural and human-made features.
Navigation is primary purpose.
U.S. Geological Survey (USGS) topographic maps. 🏅✨
History
and
map symbols
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 aware of the map's
scale
and
orientation
, both of which are tied to its
projection
.
Map scale
How much is the map reduced from the real world?
Commonly expressed on the map as 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 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
Virtual geocache
Virtual geocache
X number of locations that you need to find
using distance and bearing.
Visit this
page
to start.
Nearest geocache
From our lecture room 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.
A good clock
can tell you where you are.
Compare local time with home port time.
Your clock says 10 am
The sun is rising.
On this day 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).
Cesium clock
Cesium metal
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!
In fitness trackers?
Yep!
Strava users map military bases (whoops!)
Privacy?
Your location is a commodity
Do you mind if private companies log your location?
Do you mind if they sell it to other people?
Check your apps...
IKnowWhereYourCatLives.com
and where you do, too.
Experiment to show how much location is shared on social media
often without the poster's knowledge.
A love letter to campus
Our collaboration
We made CSVs of 650+ 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
Most 'exotic' location.
"Small cave opening at natural spring"
Smallest polygon
Most 'chosen' location.
Wildcat statue
Download your data
CSV
🔗
GeoJSON
🔗
Voronoi Polygons
🔗
Projections
US Census Report
To make the world flat
we project the sphere's latitude & longitude onto a plane.
Besides a globe, every map uses a projection.
Why?
Try using a globe to find your way around.
Measure distance and area more easily.
Coordinate systems
The globe is divided into an interval of lines
on which we make measurements.
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 cylinder, cone, or plane.
Makes a grid
with linear unit of measure.
🔍 Gotchas
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 gotchas
Primary goal: minimize distortion.
See how circles distort on different projections.
🔗
Find a suitable projection for map's scale and intent.
🔗
Take GEO309 to learn more!
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!
Mercator
EPSG: 3857
Lines of latitude and longitude are parallel.
Default projection for most web maps.
Preserves shape but distorts area.
Equal Earth
EPSG: 8857
Good projection for world maps.
Preserves area but distorts shape.
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?
Search
epsg.io
and ask us!
Why worry about projections?
It's complicated, but
when you pick the right one you can measure stuff
and cats sleep better.
Lab
Requirements
Documentation
No screen capture video
Let's do it live in class!
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?