1. Coordinate systems & projections
CS 128/ES Lecture 3b

2. Today’s dilemma – What coordinate system shall we use?
CS 128/ES Lecture 3b

3. Coordinate systems (ways to find things)
Once a projection is chosen, the map needs a coordinate grid to measure location.
Common systems:
UTM
State Plane Coordinates
CS 128/ES Lecture 3b

4. About “LatLong”
Latitude and Longitude are two coordinates used to describe a point in 3-dimensional space.
They are NOT planar
Thus, they are not easy to use on a (planar) map
Ergo, graticules1 are useful, but not for maps
1a network of parallels and meridians on a map or chart.
CS 128/ES Lecture 3b

5. Where is the Library ( )? According to Dave ( ), it is at (3, -1)
According to Ted ( ), it is at (1, 1)
CS 128/ES Lecture 3b

6. Lesson? Where you place the origin matters
Not so much to the data, but definitely in how you refer to it
CS 128/ES Lecture 3b

7. Cylindrical projections
Least distortion along line of contact
In this case equator
But nobody lives there!
CS 128/ES Lecture 3b

8. Moving the Line of Contact
If we turn the cylinder transversely and place the line of contact through Olean, then there will be little error near Bonas!
(and all points due north or south of here)
www-atlas.usgs.gov
CS 128/ES Lecture 3b

9. The Politics of Mapmaking
Problem: We might like Bonas to be the most accurate portion of the map, but folks in California may differ.
Solution: Let them use a different projection!
Create “Zones” for each region of interest
CS 128/ES Lecture 3b

10. Universal Transverse Mercator system
Based on a set of cylindrical projections running along meridians
Distortion minimized in a N – S “strip” (zone)
Zones are 8o wide but overlap by 1o on each side. 60 world wide.
CS 128/ES Lecture 3b

11. World Wide UTM Zones
CS 128/ES Lecture 3b

12. UTM coordinates
Coordinates are based on an arbitrary origin at equator and 500,000 m west of central meridian
E-W position: “easting” N-S position: “northing”
NYS has 3 zones – most state-wide datasets for New York use zone 18
CS 128/ES Lecture 3b

13. Where is Our Origin?
We “live” in UTM zone 17. Its origin is at 0˚ latitude (the equator) and 84˚ W longitude
That’s just west of Detroit, but on the equator (just off the coast of Ecuador)
If we use UTM zone 18, the boundary would be near Belmont and the origin in a suburb of Quito
CS 128/ES Lecture 3b

14. State Plane Coordinate System
Older system – usually based on Clarke 1866 ellipsoid and NAD 27 datum
Goal: distortion < 1 part in 10,000
Each state divided into either E-W or N-S zones, depending on its orientation. Most use either Transverse Mercator or Lambert Conformal projections (Alaska, New York, and Florida use both)
Only exception: Alaska panhandle (uses Oblique Transverse Mercator)
CS 128/ES Lecture 3b

15. State Plane Coordinate Zones
CS 128/ES Lecture 3b

16. An interesting concept of North?
CS 128/ES Lecture 3b

17. North? Which way is north on this map? Does this make sense?
CS 128/ES Lecture 3b

18. What is North? There are three “kinds” of north Magnetic North
Grid North
True North
CS 128/ES Lecture 3b

19. Magnetic North Pole
Lines that point to “magnetic north” point to the magnetic north pole on earth.
This location “moves”
Currently about 1000 miles off at 81.3°N,110.8°W
CS 128/ES Lecture 3b

20. Geographic North Pole
Always found at same place (90° North Latitude) Famous as home of Santa Claus.
Lines on a map that point to the geographic North pole represent “True North”
Lines on a map parallel to the central meridian represent “Grid North”
CS 128/ES Lecture 3b

21. So what’s the difference?
Declination Computation
CS 128/ES Lecture 3b

22. Who went out of their way?
Choice of projection
has a great
influence on
perception of
distance!
CS 128/ES Lecture 3b

23. Conclusions
Designing a map is like writing an essay – you can only do a decent job if you know
What you wish to convey, and
Who your audience is
With these in mind, you choose
Your projections/coordinate systems
CS 128/ES Lecture 3b