Download A coordinate system

Outline
• Datums
• Projections
• Coordinate systems
• Mapping Exercise
• GPS Coordinate Systems
Projections
Projecting Our Globe Onto A Flat Surface
Map projections are a representations of a sphere (the Earth) in two dimensions.
Globes are the most accurate way to represent the surface of the Earth. However,
because it is not practical to carry a globe into the field, map makers must figure out
how to represent a round map on a flat piece of paper, or on a flat screen.
Over the centuries many different ways of representing the round Earth on flat paper
have been developed. Each of these methods is referred to as a map projection
Projections
Projections
Orthographic Projection (Equatorial): Preserves the appearance of a globe
and shows only half the Earth at a time. Distorts shape and direction and is
useful for illustrations
Projections
Planar (Azimuthal) Projection (Lambers Equal Area Azimuthal Projection):
Used to represent the projection of a region (northern hemisphere) onto a plane
tangent to the globe, in this example, the north pole is used.
Projections
Conic Projection (Lamber Conformal Conic): Made by fitting a cone over part
of the globe. The projection depicts mid-latitudes shapes and areas well. It is
used to depict large regions up to the size of Canada
Projections
Cylindrical Projection (Mercator): is based on a cylinder tangent to the
equator. Good for equatorial regions but greatly distorted at high latitudes.
This one of the oldest and most common projections
Projections
Transverse Cylindrical Projection (Universal Transverse Mercator, UTM): is
based on a cylinder tangent to the globe along a chosen pair of opposite
meridians. The scale of the map is constant only along the central meridian.
UTM is a commonly used projection for NTS maps ranging in scale from
1:24,000 to 1:250,000. The UTM projections are based on 60 UTM Zones each
defined by a central meridian and covering 3 degrees of Longitude to the East
and West.
Scale
Large Scale Map vs Small Scale Map
Large Scale
A map which depicts a small territory is referred to as a large scale map.
Ie 1:5000 1 cm = 5000 cm
A large scale map only shows a small area, but it shows it in great detail.
Small Scale
A map depicting a large area, such as an entire country is considered a small scale
map. Ie 1:250, 000
In order to show the entire country the map must be scaled down until it is much
smaller. A small scale map shows more territory, but it is less detailed.
Coordinate Systems
A coordinate system is a means for identifying a point on the earth
on a planimetric map. The coordinates systems is typically defined
using an x- and y-ordinate or northing and easting
A choice of systems to display your location
Latitude/ Longitude - standard system of measurement
used on most maps throughout the world
Universal Transverse Mercator – UTM – newer Grid
System – gaining more acceptance
Coordinate Systems
Lat Long
The most commonly used coordinate system today is the latitude,
longitude, and height system.
The Prime Meridian and the Equator are the reference planes used
to define latitude and longitude.
If you are working with maps that cover more than 6 degrees of
longitude or are 1:1,000,000 scale or less, you will probably want to
use lat/lon coordinates.
Coordinate Systems
Lat Long
Coordinate Systems
Latitude/ Longitude - three common formats:
DDD° MM' SS.S
54° 18' 23.1” N
Degrees, Minutes and Seconds
122° 36' 52.5" W
DDD° MM.MMM
54° 18.385' N
Degrees and Decimal Minutes
122° 36.875' W
DDD.DDDDD°
54.30642° N
Decimal Degrees
122.61458° W
Coordinate Systems
Degrees, Minutes and Seconds DDD° MM' SS.S"
54° 18' 23.1" N 122° 36' 52.5" W
This is the most common format used to mark maps. It's also the most cumbersome to work with. It's a
lot like telling time…
Degrees and Decimal Minutes DDD° MM.MMM'
54° 18.385' N 122° 36.875' W
This is the format most commonly used when working with electronic navigation equipment.
Decimal Degrees DDD.DDDDD°
54 °.30642° N 122.61458° W
This is the format you'll find most computer based mapping systems displaying. The coordinates are
stored internally in a floating point data type, and no additional work is required to print them as a
floating point number.
Which format should you use?
•First off, if you are working with other people who have agreed upon a format to use, then you should
probably use that format.
•Next, you will want to look at the maps, lists of coordinates, and any software you may be using. If
you can find a consistent format among them, your work will be easier.
•You can set your GPS to display any one of these three formats. Locations can be entered into the
GPS with the selected format, and then by switching the display format setting, viewed in a different
format.
•Decimal degrees less room for confusion ( my choice)
UTM
Some of the advantages of UTM coordinates include...
• Square grids
• East-West units of measure are the same as North-South units
• No Negative numbers
• Decimal based, no fussing with minutes and seconds.
• Coordinates translate directly to distances on the ground.
• Coordinate precision is easily understood. No need to wonder
what distance a tenth of a second of longitude represents.
• It's easy to abbreviate coordinates when working in a small area.
Universal Transverse Mercator
UTM
• Gaining in popularity due to its ease of use
•UTM system divides the earth into 60 zones each 6 degrees of
longitude wide. These zones define the reference point for UTM grid
coordinates within the zone.
• UTM zones extend from a latitude of 80° S to 84° N. In the polar
regions the Universal Polar Stereographic (UPS) grid system is
used.tood. No need to wonder what distance a tenth of a second of
longitude represents.
UTM
Example 10U 512258E
5971567N
Eastings
UTM easting coordinates are referenced to the center line of the zone known as the
central meridian. The central meridian is assigned an easting value of 500,000 meters
East. Since this 500,000m value is arbitrarily assigned, eastings are sometimes referred
to as "false eastings"
An easting of zero will never occur, since a 6° wide zone is never more than 674,000
meters wide.
Minimum and maximum easting values are:
160,000 mE and 834,000 mE at the equator
465,000 mE and 515,000 mE at 84° N
Northings
UTM northing coordinates are measured relative to the equator. For locations north of
the equator the equator is assigned the northing value of 0 meters North. To avoid
negative numbers, locations south of the equator are made with the equator assigned a
value of 10,000,000 meters North.
UTM
UTM
UTM Explained
Example 10U 0512258E
5971567N
Datums
•Simply put, a datum is a model used for calculating the location of the Earth's
center. This center calculation is used as a reference point in establishing coordinate
locations, such as latitude and longitude, on the Earth's surface
•"datum" is the base reference for an X, Y coordinate system. Because the earth is
not a perfect sphere, we developed mathematical models for the accuracy of
coordinates in specific geographic areas. Known as "local datums," they use an
irregular ellipsoid model to obtain a "best fit" of the earth's surface for a particular
region
•We are lucky in that NAD83 and WGS 84 are essentially identical for our area of
North America so they can be used interchangeably
Datums
Common Datums
NAD27 - Older maps – 1927 North American Datum
NAD 83 – Newer maps – 1983 North American Datum
WGS84 – 1984 World World Geodetic System
Local Datums
ED50: European Datum 1950.
OGB36: Ordnance survey of Great Britain 1936
ADINDAN: Set of African datums
Datums
North American Datum of 1927 (NAD27) is a datum based on the Clarke ellipsoid of
1866. The reference or base station is located at Meades Ranch in Kansas. There are
over 50,000 surveying monuments throughout the US and these have served as
starting points for more local surveying and mapping efforts. Use of this datum is
gradually being replaced by the North American Datum of 1983.
North American Datum of 1983 (NAD83) is an earth-centered datum based on the
Geodetic Reference System of 1980. The size and shape of the earth was determined
through measurements made by satellites and other sophisticated electronic
equipment; the measurements accurately represent the earth to within two meters.
There are differences in the two ellipsoids ranging from 200-300 feet in the western US
to several tens of feet in the central and eastern US as show below:
NAD27 versus NAD83: the 'NAD shift' (North America)
There can be a difference (NAD27-NAD83) of up to 170 metres in y (N-S) and 70
metres in x (E-W), corresponding to the difference between the two ellipsoids
Review
A map projection is one of many methods used to represent the 3dimensional surface of the earth or other round body on a 2dimensional plane ( paper map or computer screen) in cartography
(mapmaking).
A datum is a model of the earth that is used in mapping. The datum
consists of a series of numbers and reference points that define the
shape and size of the ellipsoid and it's orientation in space. A datum
is chosen to give the best possible fit to the true shape of the Earth
A coordinate system is used to refer to a specific point on the
Earth and its corresponding point on the projected map.
Geographic – Lat long
UTM - Grid