Topic 2 A look at the Earth’s shape, coordinate systems, topographic maps, and data field analysis

Topic 2

A look at the Earth’s shape, coordinate

systems, topographic maps, and data field

analysis.

Measuring the Earth• Earth is an OBLATE SPHEROID

– Slightly flattened at the poles and bulged at the equator

– Polar Diameter: 12,714 km– Equatorial Diameter: 12,756 km– Because of this, you actually weigh

more at the poles

Proof of Earth’s Curved Surface

• “Sinking Ships”• Gravitational

Measurements• Photos from space• Altitude of Polaris

increases as you move North

Locating Places on Earth

Latitude and Longitude

Locating places on Earth• Latitude

– How many degrees above or below the Equator you are (either N or S)

– These measurements are made in Degrees (º) and Minutes (‘)

– 1 degree = 60 minutes

• Longitude– How many degrees east or west of the Prime

Meridian you are (either E or W)– These measurements are also in Degrees and

Minutes.

Latitude:• Lines of latitude are actually circles

stepping north or south to pole points• Called “Parallels”• 3 Rules:

– 1. Must be N or S of the Equator– 2. Can’t be over 90 º– 3. Numbers found on the SIDES of a map

Lines of Latitude

Finding your latitude using Polaris, the North Star

• Does not “appear” to move because it’s directly above the geographic N-pole

• The altitude of Polaris above the horizon equals your latitude (in degrees) on Earth

Altitude of Polaris (Latitude)

Longitude• Measure angular distance E or W of the

Prime Meridian

• Called “Meridians”

• 3 Rules: – 1. MUST always be E or W– 2. NEVER over 180º– 3. Number on the Top and Bottom of a map

Time zones are based on longitude

• The earth is a sphere so there are 360 degrees going around it.

• The earth rotates once in 24 hours cycling through that 360 degrees.

• 360o / 24 hrs= 15o / hour• Therefore for every hour you are away from

prime meridian time (GMT) you are 15 degrees of longitude away from there.

• If your time is earlier you’re West, later you’re East of the Prime Meridian.

Using Latitude and Longitude

• Always give LATITUDE FIRST, then LONGITUDE

• Ex. 30º N, 75 º W• Ex. 30 º 12’ N, 75 º 47’ W

New York State

Using Page 5 of your Reference Tables, What is the Latitude and Longitude of the

following?

• A. Canary Island Hot Spot

• B. Yellowstone Hot Spot

• C. Iceland Hot Spot

• D. Sandwich Plate

• E. Hawaii Hot Spot

Field:any region of space or the environment that has some measurable value or a given

quantity at every point

Alternate Definition of a Field:

• Any aspect of matter or energy that can be measured

• Examples:– Gravity, magnetism, temperature, X-ray

concentration, sound levels, elevation or depth, atmospheric pressure, wind speed, acidity of the atmosphere, relative humidity

Measuring the Fields you need to know.

• Use isolines: Def: Lines on maps used to represent areas of equal

field value.

Examples:– Isobars-lines that connect areas of equal air pressure– Isotherms-lines that connect areas of equal temp.– Contour Lines -lines that connect areas of equal

elevation on contour maps

Gradient• The rate of change over distance within a field• Usually used with topographic maps,

temperature maps and pressure maps.

Gradient=

Change in (amount of) field value

Change in distance

NOTE: Equation is on page 1 of Earth Science Reference Tables

Sample Gradient Problems:

• 1. If the elevation of Taos is 3,400 ft and the elevation of Phoenix is 1,000ft, find the gradient between them if they are 600 miles apart. 3,400’-1000’/600=4’/mi

• 2. If the temperature near the ceiling is 30 degrees C and the temperature near the floor is 22 degrees C, find the gradient if the distance between them is 12 feet. 30oC-22oC/12ft=0.67oC/foot

Getting Acquainted With Topographic Quadrangles

First things to do:

1. What SERIES map are you working with?

- series: shows you how much area

(Lat. & Long.) the map covers

-Ex: 15 minute (15’) series: Conesus

-Ex: 30 minute (30’) series: Chief Mt.

-Ex: 7.5 minute (7.5’)series: Livonia

*To determine Map Series:

Series = North Latitude – Southern LatitudeSeries = North Latitude – Southern Latitude


First things to do:

2. What is the CONTOUR INTERVAL on your quadrangle?

-Contour Interval: the number of feet

between contour lines; allows you to

determine elevation with your map

-Located at the BOTTOM CENTER of your quadrangle


First things to do:

3. What SCALE is your map drawn in?

-Scale: ratio of the distance on your map

to the actual distance on the Earth

3 Scale types:

1. Verbal: 1 inch = 62,500 inches

Therefore: 1” on map = 1 mile on Earth


Map scales con’t:

2. RF Scale

1:62,500

Map unit Land unit

Must Be The SAME UNIT

Therefore: 1” on the map = 62,500” on the

Earth’s Surface

or 1” = 1 mile on Earth


Map scales con’t:

3. Graphical Scale:the line at the bottom of your quadrangle divided into miles, feet, or kilometers

Can be used quite accurately to determine straight line distances or with a piece of string to determine curved distances

Ex: Conesus Quadrangle


First things to do:

4. How do you determine ELEVATION on a topographic quadrangle?

Elevation: Distance in feet above sea level

-Isolines (contour lines) connect points of equal elevation above sea level

-by using the contour interval and lines one can determine the elevation of features on the map


5. RULE OF V’S:

-contour lines always point upstream when they cross valleys forming a V-shape; thus water must flow the opposite direction.

-see next slide for example


6. Rule of DEPRESSIONS

-a depression contour line has hachure marks which indicate the direction in which the elevation decreases

-therefore; depression contours indicate a hole or bowl-shaped area. See “Fact Sheet” for more detail.

4050


7. Index Contour Line:

- a darker contour line which has its elevation labeled

8. Bench Mark (BM):

- a point on the map which has actually had its elevation measured and recorded

-Ex: BM452


9. Profiles

-The side-view of an area’s landscape features

-allows for upward and downward changes of a line to be shown as changes in elevation or slope

• Rules for creating profiles:– 1. Find your contour interval– 2. Find the profile line on the map which you are to

draw– 3. Place a slip of paper along the profile line and

mark the edge of it every time it crosses a contour line

– 4. Label the marks with the value of each contour line they cross

– 5. The marks are projected onto a piece of lined paper (labeled according to the contour interval) and connected with a smooth curved line

Documents

Topic 2 A look at the Earth’s shape, coordinate systems, topographic maps, and data field analysis