Locations, Latitudes, Longitudes, The Geographic Grid, Time Zones, Map Projections.

Representations of Locations and Patterns

Locations, Latitudes, Longitudes, The Geographic Grid, Time Zones,

Map Projections

Representations of Locations and Patterns• Being able to convey (or communicate) where things are, is essential to describing and analyzing aspects of Physical Geography.

• A Map is essentially a communication device

• Communicates spatial data/information through “graphic symbols” – a language of location

(Appendix B in Text)

Emergence of Cartography – the art and science of mapmaking – increasingly an automated, computerized process

However, Maps and Mapmaking have evolved over the years, becoming increasingly more complex, sophisticated, automated, and ubiquitous

The challenge has always been to represent locations and patterns on earth accurately and efficiently

A Very Early Map

Town Plan from Catal Hyük, Anatolia, Turkey, 6200 B.C.

Reconstruction of Drawing

Maps have been in existence since time immemorial – simple maps of relative locations

Early Maps

Clay tablets from Ga-Sur2500 B.C.

Interpretation of drawing

Early World Maps The world according to Herodotus 450 BC

Reconstruction of world map according to Dicaearchus (300 B.C.)

Early attempt to make locations more precise – Absolute Location

Early World Map

The first Lines of Parallels and Meridians

Eratosthenes c276 - 195 B.C.

Earth’s Dimensions :

An Oblate Spheroid or Ellipsoid (Newton, 1687)

LATITUDE AND LONGITUDELines of Parallel equate to Latitude

Latitude is measured from the Equator (00) to the Poles (900 N/S)

Lines of Meridians equate to LongitudeLongitude is measured from the Prime Meridian (00) to the International Date Line (1800 E/W)

Both Latitudes and Longitudes are measured in angular distance from the center of the earth

Together, the Lines of Latitude and Longitude constitute the Geographic Grid

Locating Los Angeles, California

Measuring Latitudes

(a) Lines of Latitude – measured in angular degrees (°) from the center of the earth, North and South of the

Equator

(b) Lines of Latitude – parallel and evenly spaced (hence, Parallels of Latitude)

Each Degree subdivided into Minutes (′), and Seconds (″)

Special Parallels and Global Latitudinal Zones

Special Parallels: Equator (0◦), Tropic of Cancer (23 ½° N), Tropic of Capricorn (23 ½° S), Arctic Circle (66 ½° N), and Antarctic Circle (66 ½° S) → Latitudinal Zones

Lines of longitude or meridians – non-parallel circular arcs that converge at the poles – measured in angular degrees (°) from the center of the earth, East and West of the Prime Meridian

Measuring Longitudes

There are 180° of longitude on either side of the Prime Meridian – which is 0°, and starts at the Royal Observatory at Greenwich, London

A degree of latitude represents a constant distance on the ground -- approx. 69 miles

or 111 km – from the equator to the poles At the equator, a degree of longitude measures about 69 miles (111 km), at 40° N or

S, 53 miles (85 km), and at the poles, 0 miles (0 km) Sextants and Chronometers – used to measure latitudes and longitudes – now

increasingly GPS

Measuring Latitude/Longitude Distances

Great Circles & Small Circles

Equator is a Great Circle: dividing the earth into two equal halves

Earth’s Rotation and Time:• Before 1884, “Local Time”

based on Solar Noon

• Now, we have Time Zones – Why?

• In 1884, International Meridian Conference in Washington, D.C. established:a) Prime Meridian (through Greenwich) – GMT and Universal

Time Coordinated (UTC) ↔ In 1972 became legal official time in all countries

b) Time Zones – 24 Zones, 15 Degrees or 1 Hour apart, 7.5 Degrees East & West of the Central Meridian of the respective zones

International Standard Time Zones

New World/North American Time Zones

International Date Line: IDL Established in the 1880s, and it follows the 180° meridian, with adjustments

The International Date Line lies directly opposite the prime

meridian, having a longitude of 180°

Crossing the line traveling east, we turn our calendar back a

full day (i.e., gain a day); Traveling west, we move our calendar forward one day (i.e., lose a day)

Latest Adjustment:Samoa & Cook Islands

Map ProjectionsThe challenge is to transfer a spherical grid (or the Geographic Grid) onto a flat surface

Visualizing the transfer of a spherical grid (or the Geographic Grid) onto a flat surface

Projections – Going from a Sphere to Flat Maps

Created by transferring points on the earth onto a flat surface. Like having a light in the center of the earth, shining through its surface, onto a projection screen (or, projection surface)

Projections now developed mathematically, using computer algorithms

There are three basic types of map projection:

(Based on the presumed positioning of projection surface)

1. Cylindrical2. Planar (or Polar or Zenithal)3. Conic (or Conical)

Cylindrical ProjectionCylindrical projection surface wrapped around the Earth; point of contact is equator

Point of contact at equator

Planar/Polar ProjectionPlanar – (Polar, Zenithal) – projection surface is a ‘flat’ surface against the Earth at a particular latitude or longitude

Conic ProjectionConic (or Conical) – projection surface is a cone, placed on or through the surface of the Earth – Where the projection surface touches the earth is the “Standard Parallel (or Line)”

Distortion – It is impossible to flatten a spherical object without some distortion in its basic attributes or properties

Map Projections try to preserve one or more of the following properties:

Area – relative representation of area size on map (for small areas).

Projections that preserve ‘area’ are “Equal Area” projections.

Shape – when meridians (longitude) and parallels (latitude) are made to intersect at right angles, shape is preserved locally.

Projections that preserve “shape” for small sections are “Conformal.”

Direction – or “azimuthality” – maintain cardinal directions (N,S,E,W).

Projections that preserve “direction” are “Azimuthal.”

Distance – variation in distance or scale on the same map ought to be minimized.

Projections that preserve “distance” are “Equidistant.”

CONFORMAL vs. EQUAL AREA: Projections can be either conformal or equal area – but not both!

Typology based on Projection Challenges

Cylindrical Projection: Mercator – A Conformal Projection

Note increasing distance between lines of latitude….why?

Watch Video: http://www.youtube.com/watch?v=AI36MWAH54s

In a Mercator projection, lines of longitude are straight vertical lines equidistance apart at all latitudes – so horizontal distances are stretched above and below the equator – more toward the poles

Mathematically stretches vertical distances by the same proportion as the horizontal distances so that shape and direction are preserved

Preserves what sailors in the 16th century needed – shapes and directions; they were willing to accept size distortion

Any straight line drawn between two points on a Mercator Projection represents a “rhumb line” – it shows true compass direction

Why Mercator? NAVIGATION!

True Compass Heading: Rhumb Line in Mercator Projection

Mercator Projection was the navigation map of choice for sailing ships: good direction, even though longer route

Polar/Planar Projection

Projection centered on the North Pole

Polar Navigation?: GNOMONIC! Any straight line

drawn on a gnomonic projection is an Arc of a Great Circle Route

◦ Great circles are represented by straight lines, making it very useful in plotting Great Circle Routes between selected destinations

Gnomonic Maps are

the navigational maps for the “Air Age”

Gnomonic projections can be either “Conformal” or “Equal Area”, but not both

Conic Conformal Projection

A better choice for mapping mid-latitude regions such as the United States is a conic projection.

Locations near the line(s) where the cone is tangent to the Earth, the standard parallel(s), will be relatively free of distortion

The Robinson Projection is among the compromise projections that uses tabular coordinates rather than mathematical formulas to make earth features look the "right" size and shape. A better balance of size and shape results in a more accurate picture of high-latitude lands like Russia and Canada. Greenland is also truer to size but compressed. It was adopted by the NGS in 1988.http://www.youtube.com/watch?v=AI36MWAH54s

Compromise Projections

Compromise ProjectionsWatch Video: http://www.youtube.com/watch?v=AI36MWAH54s

– Interrupted Case

Registration & Alignment ProblemsWhen using multiple maps of the same area, using different projectionsComputer algorithms now adjust for these problems in GIS applications.