Cartography Power i

7/31/2019 Cartography Power i

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Cartography

Introduction

Datum

-Vertical-Horizontal


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Geodetic Datums

Geodetic datums define the reference systems that describe the size and shape of the

earth. Hundreds of different datums have been used to frame position descriptions since

the first estimates of the earth's size were made by Aristotle. Datums have evolved fromthose describing a spherical earth to ellipsoidal models derived from years of satellite

measurements.

Modern geodetic datums range from flat-earth models used for plane surveying to

complex models used for international applications which completely describe the size,

shape, orientation, gravity field, and angular velocity of the earth. While cartography,surveying, navigation, and astronomy all make use of geodetic datums, the science of

geodesy is the central discipline for the topic.

Referencing geodetic coordinates to the wrong datum can result in position errors of

hundreds of meters. Different nations and agencies use different datums as the basis for

coordinate systems used to identify positions in geographic information systems, precise

positioning systems, and navigation systems. The diversity of datums in use today andthe technological advancements that have made possible global positioning

measurements with sub-meter accuracies requires careful datum selection and careful

conversion between coordinates in different datum.


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Global Systems

Latitude, Longitude, Height

oThe most commonly used coordinate system today is the latitude, longitude,

and height system.

oThe Prime Meridian and the Equator are the reference planes used to define

latitude and longitude.

oThe geodetic latitude (there are many other defined latitudes) of a point is the

angle from the equatorial plane to the vertical direction of a line normal to the

reference ellipsoid.

oThe geodetic longitude of a point is the angle between a reference plane and a

plane passing through the point, both planes being perpendicular to the equatorial

plane.

The geodetic height at a point is the distance from the reference ellipsoid to the

point in a direction normal to the ellipsoid.


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ECEF X, Y, Z

oEarth Centered, Earth Fixed Cartesian coordinates are also used to define three

dimensional positions.

oEarth centered, earth-fixed, X, Y, and Z, Cartesian coordinates (XYZ) define

three dimensional positions with respect to the center of mass of the reference

ellipsoid.

oThe Z-axis points toward the North Pole.

oThe X-axis is defined by the intersection of the plane define by the prime

meridian and the equatorial plane.

The Y-axis completes a right handed orthogonal system by a plane 90 degrees east

of the X-axis and its intersection with the equator.


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Universal Transverse Mercator (UTM)

Universal Transverse Mercator (UTM) coordinates define two dimensional,

horizontal, positions.

UTM zone numbers designate 6 degree longitudinal strips extending from 80

degrees South latitude to 84 degrees North latitude.

UTM zone characters designate 8 degree zones extending north and south

from the equator.

There are special UTM zones between 0 degrees and 36 degrees longitudeabove 72 degrees latitude and a special zone 32 between 56 degrees and 64

degrees north latitude.


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Each zone has a central meridian. Zone 14, for example, has a

central meridian of 99 degrees west longitude. The zone

extends from 96 to 102 degrees west longitude.


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World Geographic Reference System (GEOREF)

oThe World Geographic Reference System is used for aircraftnavigation.

oGEOREF is based on latitude and longitude.

oThe globe is divided into twelve bands of latitude andtwenty-four zones of longitude, each 15 degrees in extent.


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These 15 degree areas are further divided into one degree

units identified by 15 characters.


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Two numeric characters designate the integer number of minutes of

longitude east of the one degree quadrangle boundary longitude.

Two additional numeric characters designate the number of minutes

of latitude north of the one degree quadrangle boundary latitude.


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The World Geographic Reference System can be extended to refer

to larger areas of operation.

A larger East-West area can be designated by adding an "S" and thenumber of of nautical miles to the east and west sides of the

referenced point.

A larger north-south area can be designated by adding an "X" and

the number of nautical miles to the north and south.

A circular area can be designated by adding an "R" and the radius

of the circle in nautical miles.

An altitude zone can be defined by adding an "H" and a value of

altitude. The number of digits indicates the precision of the value.

Five digits implies units in feet. Four digits implies tens of feet,three digits, hundreds of feet, and two digits, thousands of feet.


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Local systems

oUniversal Polar Stereographic (UPS)

The Universal Polar Stereographic projection (UPS) is

defined above 84 degrees north latitude and south of 80

degrees south latitude.

The eastings and northings are computed using a polar

aspect stereographic projection.

Zones are computed using a different character set for south

and north Polar regions.


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National Grid Systems

oMany nations have defined grid systems based on coordinates that cover their territory.

Australia, Belgium, Great Britain, Finland , Ireland, Italy, The Netherlands, New Zealand,and Sweden are a examples of nations that have defined a National Grid System.

oBritish National Grid (BNG)

oThe British National Grid (BNG) is based on the National Grid System of England,

administered by the British Ordnance Survey.

oThe BNG has been based on a Transverse Mercator projection since the 1920s.oThe modern BNG is based on the Ordnance Survey of Great Britain Datum 1936 (Airy

Ellipsoid).

oThe true origin of the system is at 49 degrees north latitude and 2 degrees west longitude.

oThe false origin is 400 km west and 100 km north.

oScale at the central meridian is 0.9996012717

oThe first BNG designator defines a 500 km square.

The second designator defines a 100 km square.
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The remaining numeric characters define 10 km, 1 km, 100 m, 10 m, or 1 m

eastings and northings.


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oThe Irish National Grid (ING) is administered by the Irish Ordnance

Survey.

oThe ING has been based on a Transverse Mercator projection since the

1920s.

oThe ING is based on the Ordnance Survey of Great Britain Datum 1936 or

the Ireland Datum 1965.

oThe true origin of the system is at 53 degrees, 30 minutes north latitude and

8 degrees west longitude.

oThe false origin is 200 km west and 250 km south of the true origin.

oScale at the central meridian is 1.000035.

oThe first ING designator defines a 100 km square.

oThe remaining numeric characters define 10 km, 1 km, 100 m, 10 m, or 1

m eastings and northings.


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State Plane Coordinates

In the United States, the State Plane System was developed in the 1930s and was based on the

North American Datum 1927 (NAD27).

NAD 27 coordinates are based on the foot.While the NAD-27 State Plane System has been superseded by the NAD-83 System, maps in

NAD-27 coordinates (in feet) are still in use.

Most USGS 7.5 Minute Quadrangles use several coordinate system grids including latitude

and longitude, UTM kilometer tic marks, and applicable State Plane coordinates.

The State Plane System 1983 is based on the North American Datum 1983 (NAD83).NAD 83 coordinates are based on the meter.

State plane systems were developed in order to provide local reference systems that were tied

to a national datum.

Some smaller states use a single state plane zone.

Larger states are divided into several zones.

State plane zone boundaries often follow county boundaries.

Lambert Conformal Conic projections are used for rectangular zones with a larger east-west

than north- south extent.

Transverse Mercator projections are used to define zones with a larger north-south extent.

One State Plane zone in Alaska uses an oblique Mercator projection for a thin diagonal area.


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oTransverse Mercator projections are used to define zones with a larger north-

south extent.

One State Plane zone in Alaska uses an oblique Mercator projection for a thin

diagonal area.


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Public Land Rectangular Surveys

Public Land Rectangular Surveys have been used since the 1790s to identify public lands in the

United States.

The system is based on principal meridians and baselines.

Townships, approximately six miles square, are numbered with reference to baseline and principal

meridian.

Ranges are the distances and directions from baseline and meridian expressed in numbers of

townships.

Every four townships a new baseline is established so that orthogonal meridians can remain north

oriented.

Sections, approximately one mile square, are numbered from 1 to 36 within a township.

Sections are divided into quarter sections.

Quarter sections are divided into 40-acre, quarter-quarter sections.

Quarter-quarter sections are sometimes divided into 10-acre areas.Fractional units of section quarters, designated as numbered lots, often result from irregular claim

boundaries, rivers, lakes, etc.

Abbreviations are used for Township (T or Tps), Ranges (R or Rs), Sections(sec or secs), and

directions (N, E, S, W, NE, etc.).


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Metes and Bounds

Metes and Bounds identify the boundaries of land parcels by

describing lengths and directions of lines.

Lines are described with respect to natural or artificial monuments

and baselines defined by these monuments.

The metes and bounds survey is based on a point of beginning, an

established monument.

Line lengths are measured along a horizontal level plane.

Directions are bearing angles measured with respect to a previous

line in the survey.


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Miscellaneous Systems

oPostal Codes

oPostal codes such as the United States ZIP code can beused to identify areas.

oThree digit codes identify large areas.

oTexas 3-Digit Postal Zip Codes

Five-digit ZIP codes identify smaller areas.
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