1. Coordinate systems

2. Geographic Coordinate System
This is a Global Coordinate System
Based on angles on the ellipsoidal Earth
latitude
positive in n. hemisphere
negative in s. hemisphere
longitude
positive east of Prime Meridian
negative west of Prime Meridian

3. Cartesian Coordinates
Computationally, it is much simpler to work with Cartesian coordinates than with spherical coordinates
x,y coordinates
referred to as “eastings” & “northings”
defined units, e.g. meters, feet
Cartographers hate negative numbers \

4. Examples Common coordinate systems: Universal Transverse Mercator
Applicable nearly world-wide
Country-wide coordinate systems:
US – the State Plane Coordinate System
UK – Ordnance Survey National Grid

5. The Universal Transverse Mercator Coordinate System
60 zones, each 6° longitude wide
zones run from 80° S to 84° N
Coordinates within each zone must be specified
poles covered by Universal Polar System (UPS)

6. Coordinate systems
Most coordinate systems are tied to projections.

7. UTM Zone Projection Transverse Mercator Projection
Central meridian
Standard lines
Transverse Mercator Projection
applied to each 6o zone to
minimize distortion
Transverse Mercator: A cylindrical projection

8. Projection Aspects
cylindrical
conical
planar

9. UTM Coordinate Parameters
Unit:
meters
N and S zones:
separate coordinates
Each zone:
6o longitude wide
Y-origin:
equator (N zones)
near South pole* (S zones)
X-origin:
500,000 m west
of central meridian
* Actually, it’s 10,000,000 meters south of the equator

10. Universal Transverse Mercator
Each zone looks like this.
North or South must be specified (i.e. we are currently in UTM zone 17N, not just zone 17)

11. USA In The UTM Zones

12. UTM What do you do when the area of interest crosses UTM zones?
This problem is certain to occur with areas that are wider than 6° of longitude, but on some occasions even a narrower area of interest will happen to be bisected by the edge of a UTM zone
All features need to be encoded using a consistent coordinate system  it is customary to assign the coordinates to the more predominant zone that contains the majority of the area of interest

13. Universal Transverse Mercator
Nicaragua

14. UTM
It is also possibly to encounter an instance when your area of interest crosses the Equator
Northern zone: The Equator’s Northing is at 0m (the Northern zone y-origin is at the Equator)
Southern zone: The Equator’s Northing is at 10,000,000m (the Southern zone y-origin is defined as being 10,000,000m south of the Equator)
Coordinates must be consistent! 0  10,000,000
The usual solution is to assign all coordinates to the Southern zone

15. UTM
Ecuador

16. State Plane Coordinate System
The State Plane Coordinate System (SPCS) is only defined and used in the United States
Like UTM, it is divided into zones, but here zones are fully contained within states
Some larger states contain multiple zones
Original units are feet, many states are now switching to meters

17. Map Projections for State Plane Coordinate System
E-W zones:
Lambert conformal conic projection
N-S zones:
Transverse Mercator Projection

18. 4.3 Lambert Conformal Conic (Cont.)
Most states that are spread east to west use this projection.
The Lambert Conformal Conic projection does not use a single latitude line as its point of contact (a tangent line). Instead, the earth's surface intersects the cone along two lines, called secants. Along these two lines there is no distortion, but distortion does occur as the distance from the secants increases.

19. 4.3 Lambert Conformal Conic (Cont.)
                                                                                                                                                       
Distortion increases as you move away from the secant lines. (ESRI Press)

20. SPCS
The origin for each zone is placed outside the zone to the southwest (a false origin)
X-origin:
Transverse Mercator (N-S) Zones  500,000 feet west of the furthest point west
Lambert Conformal Conic (E-W) Zones  2,000,000 feet west of the furthest point west
Y-origin is not a specific distance to the south (varies by state and zone)
IS THIS TRUE??
WHERE DID JOHN GET THIS??

21. UTM vs SPCS SPCS UTM More accurate than UTM
used primarily for engineering applications, e.g. utility companies, local governments to do accurate surveying of facilities network (sewers, power lines)
Used for small areas
Difficult to use over larger areas (when multiple zones are necessary)
UTM
allows overlap between zones for mapping purposes
The UTM system is global