Datum & Coordinate Systems

Datum & Coordinate Systems

Lecture 6Lecture 6

Representing GeographyMaps

Representing GeographyMaps

Maps are a 2-D representation of RealityLegendScale (ratio of map distance: real world distance)

Directional arrowAs a 3-D world is represented in 2-D, the transformation Always involves distortion

Maps are a 2-D representation of RealityLegendScale (ratio of map distance: real world distance)

Directional arrowAs a 3-D world is represented in 2-D, the transformation Always involves distortion

DatumDatumA mathematical model that represents an approximation of the earth.

A mathematical model that represents an approximation of the earth.

Once you have a mathematical model of the size and shape of the earth, you can apply a coordinate system to in.Coordinates without a datum are vague

Datum provides an origin that gives meaning to the coordinates

Datum are errorless in AbstractWhen a datum is applied to reality, error is introduced

Once you have a mathematical model of the size and shape of the earth, you can apply a coordinate system to in.Coordinates without a datum are vague

Datum provides an origin that gives meaning to the coordinates

Datum are errorless in AbstractWhen a datum is applied to reality, error is introduced

Alexander Clarke - 1866Calculated the shape of the earth based on surveying measurements

Established the Clarke 1866 EllipsoidStandard reference for mappingUsed to create NAD27

North American Datum of 1927

NAD83 North American Datum of 1983

Uses GRS 80 Ellipsoid as it’s Base Model

Alexander Clarke - 1866Calculated the shape of the earth based on surveying measurements

Established the Clarke 1866 EllipsoidStandard reference for mappingUsed to create NAD27

North American Datum of 1927

NAD83 North American Datum of 1983

Uses GRS 80 Ellipsoid as it’s Base Model

GPS has contributed to Datum Development over timeWGS 84 - World Geodetic System 1984

the reference frame upon which all geospatial-intelligence is based

Latest update 2004

NGS - National Geodetic ServiceBrass markers are placed to pinpoint locations based on Datum

GPS has contributed to Datum Development over timeWGS 84 - World Geodetic System 1984

the reference frame upon which all geospatial-intelligence is based

Latest update 2004

NGS - National Geodetic ServiceBrass markers are placed to pinpoint locations based on Datum

Coordinate SystemsCoordinate SystemsSystems used to pinpoint a location as related to an origin

Cartesian Coordinate SystemX, Y axisBased on an originDivides an area into 4 Quadrants

Upper right (+, +)Lower left (-, -)

Systems used to pinpoint a location as related to an origin

Cartesian Coordinate SystemX, Y axisBased on an originDivides an area into 4 Quadrants

Upper right (+, +)Lower left (-, -)

UTM & State PlaneUTM & State Plane

UTM The National Imagery and Mapping Agency (NIMA) (formerly the Defense Mapping Agency) adopted a special grid for military use throughout the world called the Universal Transverse Mercator (UTM) grid. In this grid, the world is divided into 60 north-south zones, each covering a strip 6 degrees wide in longitude. These zones are numbered consecutively beginning with Zone 1. In each zone, coordinates are measured north and east in meters.

UTM The National Imagery and Mapping Agency (NIMA) (formerly the Defense Mapping Agency) adopted a special grid for military use throughout the world called the Universal Transverse Mercator (UTM) grid. In this grid, the world is divided into 60 north-south zones, each covering a strip 6 degrees wide in longitude. These zones are numbered consecutively beginning with Zone 1. In each zone, coordinates are measured north and east in meters.

State PlaneThe state plane coordinate system (SPCS)

is similar to the UTM system in many respects, but it does have some important differences. In the SPCS, each state has its own zone(s).The number of zones in a state is determined by the area the state covers and ranges from one for a small state such as Rhode Island to as many as five.

State PlaneThe state plane coordinate system (SPCS)

is similar to the UTM system in many respects, but it does have some important differences. In the SPCS, each state has its own zone(s).The number of zones in a state is determined by the area the state covers and ranges from one for a small state such as Rhode Island to as many as five.

Geographic Grid Coordinate System

Geographic Grid Coordinate System

Degrees, Minutes, SecondsDD MM SSS

Decimal DegreesDD.MMMMMMMM

OriginEquatorPrime Meridian

Degrees, Minutes, SecondsDD MM SSS

Decimal DegreesDD.MMMMMMMM

OriginEquatorPrime Meridian

LatitudeLatitude

Measured as the internal angle from an origin in the center of the earth.0 degrees - Equator90 degrees - Poles

North is PositiveSouth is Negative

Measured as the internal angle from an origin in the center of the earth.0 degrees - Equator90 degrees - Poles

North is PositiveSouth is Negative

LongitudeLongitude

Measured as a portion of the circumference of the earth.

Longitude lines are all Great Circles

Range 0 – 180 degrees

East is PositiveWest is Negative

Measured as a portion of the circumference of the earth.

Longitude lines are all Great Circles

Range 0 – 180 degrees

East is PositiveWest is Negative

Degrees, Minutes, Seconds

Degrees, Minutes, Seconds

1 Degree Latitude - 69 Miles1 Degree Longitude - 69 Miles at the EquatorConverges at the PolesIn San Diego, 1 Degree Longitude = 58.5 Miles

1 Degree = 69 Miles1 Minute (1/60 of a Degree) = 1.15 Miles

1 Second (1/60 of a Minute) = 0.01917 Miles (101.2 Feet)

1 Degree Latitude - 69 Miles1 Degree Longitude - 69 Miles at the EquatorConverges at the PolesIn San Diego, 1 Degree Longitude = 58.5 Miles

1 Degree = 69 Miles1 Minute (1/60 of a Degree) = 1.15 Miles

1 Second (1/60 of a Minute) = 0.01917 Miles (101.2 Feet)

Where is San Diego?Where is San Diego?

32o 28’ 18” N (Latitude)117o 48’ 53” W (Longitude)

Also represented as32o 28’ 18”-117o 48’ 53”

32o 28’ 18” N (Latitude)117o 48’ 53” W (Longitude)

Also represented as32o 28’ 18”-117o 48’ 53”

Decimal DegreesDecimal Degrees

Increment between lines of latitude or longitude are represented as the decimal fraction between them.

lat: 32.720939 N long: 117.151969 W

orlat: 32.720939 long: -117.151969

Increment between lines of latitude or longitude are represented as the decimal fraction between them.

lat: 32.720939 N long: 117.151969 W

orlat: 32.720939 long: -117.151969

Converting from DMS to DDD

Converting from DMS to DDD

The latitude of London expressed in DMS is 51° 29' 16" North. To convert this location to DD, follow these steps:

1. Divide each value by the number of minutes (60) or seconds (3600) in a degree:

29 minutes = 29/60 = 0.4833 degrees16 seconds = 16/3600 = 0.0044 degrees

2. Add up the degrees to get the answer:51° + 0.4833 ° + 0.0044 ° = 51.4877 DD

The latitude of London expressed in DMS is 51° 29' 16" North. To convert this location to DD, follow these steps:

1. Divide each value by the number of minutes (60) or seconds (3600) in a degree:

29 minutes = 29/60 = 0.4833 degrees16 seconds = 16/3600 = 0.0044 degrees

2. Add up the degrees to get the answer:51° + 0.4833 ° + 0.0044 ° = 51.4877 DD