Mapping the Earth

• Differentiate between planimetric and hypsometric maps• Define/describe map projections• Identify common projection shapes• Define/describe an undevelopable surface • Identify where distortion is minimized and maximized in different types of projections• Describe why a Mercator projection distorts area towards the poles.• Define/describe: cartographic scale, ecological scale, grain, extent, representative fraction• Explain why maps are models • Explain the differences between a large and small cartographic scale in terms of detail

and surface area represented. • Match locations according to their latitude and longitude• State the latitude and longitude for Lexington• State the latitude and longitude for the Tropic of Cancer, the Tropic of Capricorn, the

Arctic Circle, and the Antarctic Circle• Explain how time zones are designed• Explain UTC time• Describe the difference between geographic and magnetic north

Objectives

What is a map?• A map is a model used to convey patterns of

physical or human processes and patterns• Maps are idealized representations of reality.

• General map formats:

– Mental or cognitive maps– Hardcopy (paper) maps– Virtual (digital code) maps

Mental maps

Paper maps

Digital maps

Digital maps

Map information

• Planimetric – Two-dimensional information

• Hypsometric – Two dimensions plus a third dimension– Third dimension is typically relief or topography– Ways of depicting relief

• Shading• Contour lines

9. Maps invokesymbolism

The contour interval is 20 ft. Point elevations are:A = 700 ftB = 740 ftC = 770 ftD = 820 ft

Uphill direction

Slow change in elevation. Contour linesfar apart.

Rapid change in elevation. Contour linesclose together.

Types of contour maps

• Topographic (terrestrial elevation)• Bathymetric (sea floor elevation)• Isohyets (rainfall)• Isopachs (rock or sediment thickness)• Isotachs (wind speed)• Isobars (air pressure)• Geopotential heights (altitude of a given air

pressure)

Topographic map

Match the letter and number

Bathymetric maps (ocean floor relief)

Isobaric maps (air pressure)

Individual lines are called isobars.

Isobars (solid yellow lines)

This is a strong low pressure system, which produced largeamounts of snow and wind across the eastern US.

In an isobaric map, where isolinesare close together, winds are the strongest. Winds are strongest in Virginia, North Carolina,and West Virginia.

Isohyets(precipitation)

Colored areas represent isotachs, lines encompassing areas of equal windspeed. Contour interval = 10 knots

Green lines are geopotential heights, the altitude at which one reaches 300 mb in air pressure. For example, 9720 represents 9720 meters. 300 mb in air pressure is reached when altitude is 9720 meters or about 32,000 ft.

Isotach (wind speed)

Geopotential height maps (constant pressure surface)

The blue lines are geopotential heights. Contour interval is 60 meters. This is a map of the 300 mb geopotential heights.

How high would you have to go up to reach 300 mb over Kentucky?

Note that the wind barbs in this map convey the direction of wind flow.

Geopoential heights

Isopach maps (contour interval = 5 ft for the one above) show the thickness of rock layers or other subsurface feature. In this map they show the thickness of a rock layer known to produce oil. The round symbols are oil well locations and the depths (6000 – 7000 ft) drilled to reach oil. Why would oil drillers want to know the thickness of an oil-bearing rock layer?

Isopach map showingthickness of the limestonecomprising the Florida Aquifer

Isopach map showingthickness of hydrocarbon-bearing strata in western Kentucky.

Map projections• A projection is any number of

cartographic models used to project the Earth’s curved surface as a flat surface

Why don’t we just use a globe instead of flat maps?

• Globes are virtually ideal models of the world:– Correct shape– Correct area– Correct distances– Correct direction

Because, globes are:

• Impractical • Expensive to manufacture• Difficult to plot routes on a

curved surface• Users are overhead of a

single point (perspective view). They do not have an orthographic view (directly overhead of all points)

What are the tradeoffs for projecting the globe onto a map?• A sphere is an undevelopable surface.

An undevelopable surface cannot be flattened into two dimensions without some distortion.

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Cylindrical projection

Types of projections

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Conic projection

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Planar projection

Distortion from projection

• Every map projection distorts at least three and sometimes all four, of the following properties: shape, area, distance, and direction

• No projected maps can have both true shape (conformality) and true area (equivalence).

The Mercator projection distorts area (look at Greenland),but shape is true

distortionellipses

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Conformal (true shape) map projection

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Equivalent (true area) map projection

Compromise projections

Cartographic scale

Cartographic scale

• Map scale is the ratio of the size of an object on a map to its actual size

• Map scale is expressed with a representative fraction (RF): – 1:50,000– 1:10,000

• These can be interpreted as: 1 inch = 10,000 inch or 1 cm = 10,000 cm. Any unit can be used so long as they are on both sides of the equation.

Cartographic scale

• Assuming that you have two maps of the same paper size, which of the two RFs shows the most detail and the smaller surface area?

1:50,000 1:10,000

Impact of cartographic scale on representation of data

1:250,000 1:50,000 1:2,500

Operational scale

Spatial andtemporal dimensionof an object or process

Scale at which observations and measurements take place

Ecological scale: grain and extent

Parallels run EW but are measured NS.

Meridian run NS but are measured EW

Meridians (lines of longitude) converge at poles

The distance spanned by a degree of longitude varies enormously between the Equator and the poles.

The geographic grid

Arctic Circle: 66.5 degrees NAntarctic Circle: 66.5 degrees STropic of Cancer: 23.5 degrees NTropic of Capricorn: 23.5 degrees S

Magnetic declination: the difference in angle between a magnetic pole and a geographic pole (true north).

True north vs magnetic north

Time zones

24 hours divided by 360 degrees equals 15 degree span for each time zone.

Military (24 hour time)

UTC time – Coordinated Universal Time or Z time

Calculating local standard time from UTC in Lexington

• From March 13, 2016 to Nov 6 2016– This is during daylight savings time, when we set our

clocks ahead one hour to take advantage of the longer hours of daylightUTC time - 4 hours = LST (on 24 hour clock)

• From Nov 6, 2016 up until March 12, 2017 – We set our clocks behind one hour to give us more sunlight

in the evening. We are no longer on daylight savings timeUTC time – 5 hours = LST (on 24 hour clock)

Romford, England Ropsha, Russia Rosales, Mexico Rosetown, Canada

What is the latitude and longitude for Lexington in minutes and degrees? 30" N and 84" W

51" 33' N 108" 00' W59" 44' N 29" 53‘ E28" 15' N 100" 43' W 51" 35' N 0" 11' E

Match the locations with their correct lat and long:

Practice

Practice

• On Sept 2 if it is 10Z, then it is 6:00 hours or 6 am here in Lexington.On Sept 2 if it is 22Z then it is 18:00 hours or 6 pm here in Lexington

• On Dec 3 if it is 10Z then it is 5:00 hours or 5 am here in Lexington.

• On Dec 3 if it is 4Z, then it is 23:00 hours (the day before) or 11 pm here in Lexington.

8/23/16 00UTC 048 HR FCST VALID MON 8/25/16 00 UTC NCEP/NWS/NOAA

When was this forecast model made in local Lexington time/day/date? When is this prediction valid in local Lexington time/day/date