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
Getting Acquainted With Topographic Quadrangles
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
Getting Acquainted With Topographic Quadrangles
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
Getting Acquainted With Topographic Quadrangles
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
Getting Acquainted With Topographic Quadrangles
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
Getting Acquainted With Topographic Quadrangles
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
Getting Acquainted With Topographic Quadrangles
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
Getting Acquainted With Topographic Quadrangles
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
Getting Acquainted With Topographic Quadrangles
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
Getting Acquainted With Topographic Quadrangles
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