PROJECTIONS, COORDINATE SYSTEMS, AND
DATUMS - EXPLAINED
Ohio Geospatial Technology Conference for Agriculture
and Natural Resource Applications
March 26, 2003
David Conner
National Geodetic Survey
Geodetic Advisor to the State of Ohio
Dave.Conner@noaa.gov (614) 292-1619
www.ngs.noaa.gov
1
The geodetic layer is the key to a GIS
Strong GIS/LIS
and engineering
systems require
well determined
coordinate
systems and
accurate spatial
references
2
The Shape of the Earth
• Earth is not flat
• Earth is not a sphere
• An ellipsoid is a simplified model of
Earth’s shape
• A datum is a set of reference locations,
including elevations, describing more
precisely the surface of the Earth
3
Earth Models & Datums
Ellipsoid – Geoid relationship
H = Orthometric Height (NAVD 88)
h = Ellipsoidal Height (NAD 83)
H
N = Geoid Height (GEOID 99)
H h
TOPOGRAPHIC SURFACE
N
Sea Level
Ellipsoid
GRS80
=h-N
Geoid
4
Common Ellipsoids and Datums
NAD27 (North American Datum of 1927): A system
derived from land-based surveys, using the Clarke
(1886) ellipsoid.
NAD83: A satellite-based system using the center of
the earth as a reference point using measurements
taken in 1980, and adopted internationally as GRS80
(geodetic reference system 1980).
WGS84 (World Geodetic System 1984): A refinement
of GRS80 used by the US military (and therefore by
GPS).
For most geographic purposes, NAD83, GRS80, and
WGS84 are equivalent.
5
Projection types
• Projections convert spherical coordinates (latitudelongitude) to planar coordinates.
• Three fundamental types of projections:
– Azimuthal: projection onto a planar surface
– Cylindrical: projection onto a cylinder, which is then
‘unrolled’ to a plane.
– Conic: projection onto a cone, which can be unrolled to
a plane.
• All projections create distortions of either shape,
area, distance, or more than one of these.
6
Three common coordinate
systems used in GIS
• Geographic (Lat-Long)
• UTM (Universal Transverse Mercator)
• State Plane Coordinate System (SPCS)
SPCS Projection is either Transverse Mercator (cylindrical) or
Lambert (conic)
7
UTM
• Worldwide system with units in meters
• In northern hemisphere, Y-coordinate (northing) is
distance in meters from the Equator.
• X-coordinate (easting) is distance in meters east from
a central meridian for a zone (negative values west of
the central meridian).
• Consists of 60 zones, each 6 degrees wide.
8
State Plane Coordinates (SPCS)
• Specific system for each state
• Some states divided into multiple zones
with different grid systems for each zone.
• Ohio has two zones: north and south
• Most property maps (plat maps; tax maps),
zoning maps, etc. are in State Plane
Coordinates.
9
State Plane Coordinates - Units
NAD 27 - Coordinates in U.S. Survey Feet
NAD 83 - Coordinates Metric w/State Defined Foot Conversion
1 Meter = 3.280833333 U.S. Survey Feet
1 Meter = 3.280839895 International Feet
Difference is ~ 1:500,000
U.S. Survey foot in Ohio
10
STATE OF OHIO
Bob Taft, Governor
DEPARTMENT OF NATURAL RESOURCES
Samuel W. Speck, Director
DIVISION OF GEOLOGICAL SURVEY
Thomas M. Berg, Chief
LATITUDE-LONGITUDE GRID, UTM ZONE BOUNDARY, AND
STATE PLANE COORDINATE SYSTEM ZONE BOUNDARY
84°
85°
42°
83°
82°
81°
80°
ASHTABULA
WILLIAMS
FULTON
LUCAS
LAKE
OTTAWA
GEAUGA
WOOD
HENRY
SANDUSKY
DEFIANCE
TRUMBULL
CUYAHOGA
ERIE
LORAIN
PORTAGE
PAULDING
41°
HURON
SENECA
PUTNAM
MEDINA
SUMMIT
HANCOCK
MAHONING
VAN WERT
WYANDOT
CRAWFORD
RICHLAND
ASHLAND
WAYNE
STARK
ALLEN
COLUMBIANA
HARDIN
CARROLL
MERCER
MARION
AUGLAIZE
HOLMES
MORROW
TUSCARAWAS
LOGAN
SHELBY
KNOX
JEFFERSON
UNION
COSHOCTON
HARRISON
DELAWARE
DARKE
LICKING
CHAMPAIGN
GUERNSEY
MIAMI
BELMONT
MUSKINGUM
FRANKLIN
MADISON
40°
CLARK
PREBLE
FAIRFIELD
NOBLE
PERRY
MONTGOMERY
MONROE
GREENE
PICKAWAY
MORGAN
FAYETTE
HOCKING
BUTLER
WARREN
WASHINGTON
CLINTON
ROSS
ATHENS
VINTON
HIGHLAND
HAMILTON
CLERMONT
MEIGS
PIKE
JACKSON
39°
BROWN
GALLIA
ADAMS
SCIOTO
N
LAWRENCE
0
10
20
30 miles
0 10 20 30 40 kilometers
38°
UTM
ZONE 16
UTM
ZONE 17
STATE PLANE NORTH
STATE PLANE SOUTH
11
GEOGRAPHIC POSITION (Lat-Long)
Variation Between Datums: NAD27 vs NAD83
1927 North American Datum
To place on the predicted North American Datum 1983
move the projection lines 4 meters south and
6 meters west as shown by dashed corner ticks.
12
NAD 27 and NAD 83
Two Horizontal Datums
13
NAD 27 to NAD 83 (1986) Position and Coordinate Shifts
Geodetic vs State Plane
CLARK 1928
Geodetic Position
Latitude
NAD 27
NAD 83 (1986)
Difference
Longitude
40 03 09.89400
40 03 10.12158
-0.22758
82 58 35.2650
82 58 34.92303
-0.34197
North 23.06 ft
East 25.17 ft
Overall position shift of 34.14 ft NE
State Plane Coordinates
NAD 27
NAD 83 (1986)
Difference
Northing (Y)
748,005.80 ft
748,034.32 ft
+
37.52 ft
Easting (X)
1,866,612.19 ft
1,835,142.41 ft
- 31,469.78 ft
Overall shift is 6 miles East
14
NGVD 29 and NAVD 88
Two Vertical Datums
15
Datum Transformation Software
Federally produced datum transformation software is
available free of charge from NOAA’s National Geodetic
Survey.
http://www.ngs.noaa.gov/TOOLS/
NADCON – NAD 83 vs NAD 27
VERTCON – NAVD 88 vs NGVD 29
HTDP – between a wide variety of reference frames
UTMS – UTM vs lat/long
SPCS83 – State Plane 83 vs lat/long
GPPCGP – State Plane 27 vs lat/long
NATIONAL OCEAN SERVICE
16
METADATA
METADATA IS DATA ABOUT DATA
DATUMS Horizontal including adjustment tag
NAD 27, NAD 83(1986), NAD83 (199X), NGVD29, NAVD88
Geoid Model for GPS derived orthometric heights
GEOID96, GEOID99
UNITS
Meters, U.S. Survey Feet, International Feet
ACCURACY
A, B, 1st, 2nd, 3rd
or… 10 m, 1 m, 0.1 m, 3cm, 1cm
17
http://www.ngs.noaa.gov/cgi-bin/datasheet.prl
National Geodetic Survey,
Retrieval Date = MARCH 21, 2003
KZ1585 ***********************************************************************
KZ1585 DESIGNATION - SHANNAHAN
KZ1585 PID
- KZ1585
KZ1585 STATE/COUNTY- OH/DELAWARE
KZ1585 USGS QUAD
- POWELL (1988)
KZ1585
KZ1585
*CURRENT SURVEY CONTROL
KZ1585 ___________________________________________________________________
KZ1585* NAD 83(1995)- 40 09 24.94135(N)
083 00 26.03461(W)
ADJUSTED
KZ1585* NAVD 88
296.307 (meters)
972.13
(feet) ADJUSTED
KZ1585 ___________________________________________________________________
KZ1585 X
594,316.727 (meters)
COMP
KZ1585 Y
- -4,845,377.251 (meters)
COMP
KZ1585 Z
4,091,487.584 (meters)
COMP
KZ1585 LAPLACE CORR-3.19 (seconds)
DEFLEC99
KZ1585 ELLIP HEIGHT262.49 (meters)
(04/01/98) GPS OBS
KZ1585 GEOID HEIGHT-33.85 (meters)
GEOID99
KZ1585
KZ1585 HORZ ORDER - FIRST
KZ1585 VERT ORDER - FIRST
CLASS I
KZ1585 ELLP ORDER - FOURTH
CLASS I
.
.
.
.
.
KZ1585
KZ1585;
North
East
Units
Scale
Converg.
KZ1585;SPC OH N
54,568.670
556,782.294
MT 1.00006442 -0 19 59.6
KZ1585;SPC OH S
239,579.155
556,783.904
MT 1.00002679 -0 19 18.7
KZ1585;UTM 17
- 4,447,106.432
329,050.199
MT 0.99995976 -1 17 41.1
KZ1585
KZ1585
SUPERSEDED SURVEY CONTROL
KZ1585
KZ1585 NAD 83(1986)- 40 09 24.94900(N)
083 00 26.04100(W) AD(
) 1
KZ1585 NAD 27
- 40 09 24.72300(N)
083 00 26.37800(W) AD(
) 1
KZ1585 NGVD 29
296.464 (m)
972.65
(f) ADJ UNCH
1 1
KZ1585
KZ1585.See file *dsdata.txt to determine how the superseded data were derived.
*dsdata.txt = Metadata for all datasheet information
18
Good Geographical Information Systems
begin with good coordinates
GEOGRAPHY WITHOUT GEODESY IS A FELONY
19
20
Adjustment tags
NAD83 has been readjusted periodically
with most states having 2 or 3
adjustments with a final national
adjustment planned in 2005.
Each time this happens a small number of
points are held fixed at the best values
available at the time
In general each readjustment will result in
new coordinates for all points in the
effected area.
2005 Nationwide adjustment <5 cm change
21
PLANE COORDINATE SYSTEMS
STATE PLANE AND UNIVERSIAL TRANSVERSE
MERCATOR GRID COORDINATES ARE A DIRECT
MATHEMATICAL CONVERSION FROM LATITUDE
AND LONGITUDE TO A CARTESIAN NORTHING
AND EASTING (Y & X) COORDINATE SYSTEM,
AND MUST MAINTAIN THE SAME DATUM TAG
[e.g. NAD 83(1993)] AS THE LATITUDE AND
LONGITUDE
NATIONAL OCEAN SERVICE
22
STATE PLANE COORDINATE SYSTEMS
NOAA Manual NOS NGS - 5 “State Plane Coordinate System of 1983”
Lambert Conformal Conic and Transverse Mercator Projections
International, State and County Boundaries
Zones Approximately 158 miles wide
NAD 27 - Coordinates in U.S. Survey Feet
NAD 83 - Coordinates Metric w/State Defined Foot Conversion
1 Meter = 3.280833333 U.S. Survey Feet
1 Meter = 3.280839895 International Feet
U.S. Survey foot in Ohio
23
Datums for GIS spatial references
• All geodetic data has a datum and adjustment tag
associated with it
Ex: NAD83 (1995)
NAD83 (1986) SPC OH N
24