Transcript Geographic Coordinate System

Review of Projections and
Coordinate Systems
Referencing Data to Real Locations
Coordinate Systems
Geographic vs. Projected
Geographic Coordinate Systems
(GCS)
Location measured from curved surface
of the earth
Measurement units latitude and longitude
– Degrees-minutes-seconds (DMS)
– Decimal degrees (DD) or radians (rad)
Projected Coordinate Systems (PCS)
Flat surface
Units can be in meters, feet, inches
Distortions will occur, except for very fine
scale maps
Geographic Coordinate System
•Parallels - east to west – 0° at the Equator (0 °-90 °)
•Meridians – north to south – 0° at the Prime Meridian (0 °-180 °)
•Latitude and longitude are angular measurements made from
the center of the earth to a point on the surface of the earth
Map Projection:
A map projection is a
mathematical formula for
representing the curved surface
of the earth on a flat map.
– wide variety of projections
possible
– each projection will create a
different type of distortion
Distortions
Distortions are inherent in maps
The Earth is round, a map is flat
distance
area
shape
direction
Map Projections Types
P lanar P rojection
C onical P rojection
C ylindrical P rojection
14
Datums
A reference frame for locating points on
Earth’s surface
It consist of:
1) A spheroid (ellipsoid) with a spherical
coordinate system and an origin.
2) A network of points that have been
meticulously surveyed.
Modeling the Earth : spheroids,
ellipsoid and datums!
– North America Datums
NAD 27
– Clarke 1866 spheroids
– Meades Ranch, KS
– Local Datum
NAD 83
(National Geodetic Survey)
– GRS80 (Geodetic Reference System) spheroid
– Earth-centered
– GPS compatible
WGS84 (National Imagery and Mapping Agency – National
Geospatial – Intelligence Agency)
– Additional parameters of model
– Used in GPS
Why all the trouble to learn about datums?
10- 100 meter shift between NAD 27 and NAD83/WGS 84!
Working with Coordinate Systems in ArcGIS
On-the-fly projection
“Define Projection” vs “Project”
Predefined Projections (provided by
ArcGIS)
Projection File - .prj
– Text file stores projection information
Data frame takes on the CS of the first
data layer added to the project.
Map Projections Parameters
Standard Line – line of tangency - where the projection
surface meets the globe
•No distortion at this point – increase distortion moving
away
•Standard Parallel
•Standard Meridian
•More than one standard line possible
•Central Line
•Defines the center of the map projection
•Central parallel - latitude of origin
•Central meridian
•Can be different from standard line
•False Easting – x- coordinate value
•False Northing – y- coordinate value
14
Commonly Used Map Projections
in California
Universal Transverse Mercator (UTM)
California State System
– (Teale) Albers Equal-Area Conic
State Plane Coordinate (SPC) System
– Lambert conformal conic projection
Teale Albers Projection ( California)
AKA: CA State System,
CA Albers Equal Area
Projection Surface: Conical
Spatial Properties: Equal Area
(Equivalent)
Projection Parameter
1st Standard Parallel: 34° 00’ 00’’
2nd Standard Parallel: 40° 30’ 00’’
Central Meridian: -120° 00’ 00’’
Central Parallel
Latitude of origin: 00° 00’ 00’’
False easting (meters): 0
False northing (meters): -4,000,000
Example of Coordinate:
X = -161,327 (meters)
Y = -149,199 (meters)
Universal Transverse Mercator (UTM)
60 zones
– 6o wide
– Defined by central meridian (example: 120° W)
Preserves direction and small shapes
(conformal projection).
Extent is from 84°N to 80 °S.
84 N°
80 S°
UTM coordinates are easily recognized by 6
digit for the x, and 7 digit for the y ( most of
the time at latitudes of 15° and greater in the
Northern Hemisphere)
Secant!
Universal Transverse Mercator (UTM)
UTM Zone 10 N and S
Projection Parameter
False Easting: 500, 000m
False Northing: 0 m
Central Meridian: -123°
Scale Factor: 0.999600
Central Meridian
Value Decrease
Value Increase
Value Increase
Projection Surface: Cylindrical
Spatial Properties: Conformal,
Shape and Direction
False Easting 500,000
0m
0m
10,000,000 m
Equator Origin
Value Increase
Example of Coordinate in
Monterey:
X = 602,585 (meters)
Y = 4,050,086 (meters)
84 N°
80 S°
6°
UTM
Often found in military applications, and in
datasets with global or national coverage
UTM system is secant with lines of scale 1
located on both sides of the central meridian,
the projection is conformal, so small features
appear with the correct shape and scale is
the same in all directions. (Scale is 0.9996 at
the central meridian and at most 1.0004 at
the edges of the zones
Because there are effectively 60 different
projections, maps will not fit together across a
zone boundary.
Universal Transverse Mercator (UTM)
State Plane Coordinate System
State Plane Coordinate System (SPSC)
Although distortions of the UTM system are small,
they are too great for accurate surveying
Plus zone boundaries follow arbitrary lines of
longitude rather than jurisdictions.
 Not a true map projection
Collection of different projections for every state in the
US
Designed in the 1930s to provide a local reference
system tied to a national datum.
Some states (depending on size and latitudinal extent)
have multiple zones
Most USGS 7.5 minute maps indicate state plane
coordinates (as well as UTM, and lat-long grid)
Cadasters
and the US Public Land Survey System
The cadaster is defined as the map of land
ownership in an area, maintained for the
purposes of taxing land, or of creating a public
record of ownership.
Parcels of land in a cadaster are often uniquely
identified by number or by code.
The State Plane Coordinate System
East-West oriented States (or zones) use the
Lambert Conformal Conic projection (ex.
Tennesse)
North-South oriented States (or zones) use
the Transverse Mercator projection (ex.
Illinois)
One zone in Alaska uses Oblique Mercator
Based on the North American Datums:
NAD27 and NAD83
Reference is in Eastings and Northings
SPCS
State Plane Coordinate System for
California
AKA: Lambert Conformal Conic
Projection Surface: Conical
Spatial Properties: Shape and
Distance
Projection Parameters
False Easting: 6561666
False Northing: 1640416
Central Meridian: -119 °
Standard Parallel_1: 36.00 °
Standard Parallel_2: 37.25°
Latitude Of Origin: 35.33 °
Example of Coordinate in
Monterey:
X = 5,798,378 (feet)
Y = 2,135,524 (feet)
State Plane Zones for NAD 1927 and 1983