ES.3 The student will investigate and understand how to read and interpret maps, globes, models, charts,
and imagery. Key concepts include
a) maps (bathymetric, geologic, topographic, and weather) and star charts
Note: These tools are used in various units to aid in content instruction. The only one that I teach separate
from content is topographic maps. They can then be used to aid in instruction in other units.
Topographic maps (a.k.a. contour maps) are two dimensional representations of the shape of the land
surface (topography). Contour lines connect points of equal elevation above sea level. Two different
contour lines can never intersect. This would mean that one point has two different elevations. The
shoreline of a continent or an island is the 0 contour. Contour lines are drawn at uniform vertical elevations
above sea level. Imagine the water level rising in constant increments. The new shoreline would represent
the next highest contour line. The vertical distance between two adjacent contour lines is called the
contour interval. The most common intervals in U.S. maps are 10, 20, and 40 feet. In rugged terrain,
larger contour intervals are used.
Hills are represented by concentric contour lines, like an irregular bull’s eye. On any given map, more
concentric circles in a hill denote a taller hill. Each smaller circle is one contour interval higher than the
previous larger circle. Examine the map below, identify the three tallest hills, and number them from 1 to 3,
with 1 being the tallest. Find a common countour line, such as the dark 900 ft line on hill A & B below.
C
B
A
http://mapserver.maptech.com/bp/mapserver/index.cfm
In order from tallest down, the hills are labeled A, B, C.
Contour lines make V’s when they cross a stream. The V’s point toward higher elevations or the source of
the water in the stream. Think of the V as being a cup from which the water pours. In the above map,
Tussocky Creek is flowing from the two ponds in the SE toward the NW, from the point of one V to the point
of the next V.
When contour lines are closely spaced, it means the land is changing elevation in a very small distance, i.e.
the land is steep. When contour lines are far apart, the land is less steep. A careful examination of the
map above shows that the contour lines are farther apart near the top of hills, indicating that they are very
rounded and relatively flat on top. The steepest land is along the sides of the valleys, on either side of the
creeks, especially the unlabeled stream in the NE.
Spot elevations are given on maps with a benchmark (BM) or an X with a number beside it. On the above
map there are two clearly labeled spot elevations and one road intersection elevation is given. Locate
these elevations. Note that they are not on contour lines and do not have to end in zero.
Every fifth contour line is darker and is numbered. To find the elevation of a point on a contour line, identify
the nearest numbered line and count up or down by contour intervals. You can tell uphill direction from a
downhill direction over a small distance by considering at least two of the following criteria:
(1) Uphill is in the direction of smaller circles.
(2) Uphill is away from water.
(3) Uphill is in the direction V’s in valleys point.
(4) Uphill is toward larger numbers.
Points between contours can be estimated by mentally dividing the space between adjacent contours into
10 equal segments and following the procedure outlined above. This is a basic number line skill from math.
Bathymetric maps are simply topographic maps of the seafloor. Elevations are given as feet below sea
level, otherwise, the same rules apply. Many websites, such as the one below, give bathymetry as color
coded, and give a physiographic rendition (more artistic than scientific).
http://www.ngdc.noaa.gov/mgg/image/2minrelief.html
Geologic maps show what rocks are found at the surface of the earth under the layer of soil. The rock
layers are color coded. The legend of the map tells the age and the type of rock represented by that color.
Faults, folds, and unconformities can be identified from the patterns produced. There are more detailed
maps out there which give the orientation of rock layers and details about faults, but that is overkill for high
school.
Example of a simplified geologic map of Virginia:
There will be more presented under the SOL for the geologic history of Virginia. For now, this link is a great
clearing house for geologic maps of Virginia.
http://geology.about.com/od/geology_va/Virginia_Geology.htm
There is a huge variety of weather maps from those showing just national temperature distributions with
color isotherms (contour lines on temperature) to those showing detailed weather data for various recording
stations. For beginners, this web site provides more detailed information on reading weather maps.
http://ww2010.atmos.uiuc.edu/(Gh)/guides/maps/home.rxml
Star charts show the appearance of the night sky at a specific location and time. They show various
celestial objects: constellations, planets, moon, deep space objects (nebula, galaxies) etc. The web page
below shows an oriented star chart for any location, date, and time you specify.
http://www.fourmilab.ch/yoursky/
b) imagery (aerial photography and satellite images);
Analysis of imagery requires an understanding of the general principles of remote sensing. The most
familiar imagery is just a photograph made from an airplane. There is actually very little information present
in a photograph compared to a remote sensing image, but it is easiest for students to understand. Only
visible light is recorded on film. Satellite imagery is digital and records a wide variety of electromagnetic
radiation in different bands (range of wavelengths). In producing an image, different bands can be selected
for their information. A digital image is made up of small squares called pixels. The important point to get
across to students is the concept of resolution, which depends on the pixel size. Resolution determines the
size of the smallest object that can be identified in the photograph or image. In traditional photography, this
depends on the lens, the film, and the grain of the paper. In digital imagery, it depends on the pixel size,
which can vary from a half a meter up to tens of kilometers.
In imagery, the average intensity of radiation in different bandwidths (range of wavelengths) is recorded for
each pixel. This is translated into grayscale when an image is made. In a false color image, a color is
assigned to each bandwidth. Several bandwidths can then be shown on a single image. The same
principles apply to digital imagery from telescopes. The images below of the crab nebula illustrate the
different information recorded in different bandwidths.
Crab Nebula in visible light
False color Crab Nebula: red – radio waves; greenvisible light; blue – x-rays
False color Crab Nebula: blue – x-rays; red visible
False color Crab Nebula: blue - x-rays; green visible; red - infrared
Note that the second image above conveys the information that during a supernova, the wavelength of light
decreases, since all light travels at the same speed.
Image source: http://apod.nasa.gov/apod/astropix.html
For more than you could possibly want to know about remote sensing visit this online tutorial:
http://rst.gsfc.nasa.gov/Front/tofc.html
For a source of satellite images of earth and a subscription to a weekly newsletter with images, go to this
web site:
http://earthobservatory.nasa.gov/
The website listed below has satellite and air photographs at various resolutions of most locations in the
United States. It is instructive to put in the latitude and longitude of your high school and have students
zoom in to higher resolutions (smaller objects visible) to see what features become more and more
discernable.
http://terraserver.microsoft.com/
This web site is definitely worth a visit. You can find digital topographic maps at different scales. You can
also use this to find the latitude and longitude of any place on the map.
http://mapserver.maptech.com/bp/mapserver/index.cfm
c) direction and measurements of distance on any map or globe;
Direction can be specified in either of two ways: cardinal directions (north, south, etc) or bearings. True
north (as opposed to magnetic north) or south is parallel to lines of longitude. East or west is parallel to
lines of latitude. The compass rose is divided into a 360° circle which gives bearings. Generally speaking,
unless there is information to the contrary, north is assumed to be at the top of the map and corresponds to
0 or 360° in bearings. East is to the right of north and corresponds to 90°; south is at 180° and west at
270°. Northeast (NE) is half way between north and east and would have a bearing of 45°. On a map, a
circular protractor can be laid over one point, with 0 or 360 toward north, and the bearing of a line to
another point can be read directly.
Students may have some difficulty with the way compass directions are phrased. It is important to know
that when we say that point B is NW of point A, that we are standing on A, looking to B and we are facing
NW. Have students locate places on a map by describing their position on the map in terms of cardinal
directions.
Measurement of distance on a map requires the use of a scale. The scale of a map is a ratio of distance
on the map compared to distance on the ground. There are generally two kinds of scales on topographic
maps: graphic scale and a numeric scale.
The graphic scale is a line given that represents a set distance on the ground and can be used directly to
approximate ground distance from map distance. Either the distance between two points can be measured
with a ruler or marked on a piece of paper and the ruler or the paper can then be laid alongside the graphic
scale and the ground distance is estimated.
The numeric scale is a numeric ratio such as 1:24000. This means that 1 centimeter measured on the map
represents 24000 centimeters on the ground. Any units could be used, inches, feet, etc. To find ground
distance between two points, just measure the distance on the map in centimeters. Multiply this
measurement by the number to the right of the colon to obtain ground distance in centimeters. The
resulting number can then be converted into more meaningful units such as kilometers or miles. The
numeric scale will be printed on most maps in the legend.
d) location by latitude and longitude and topographic profiles
For many students, this is the most difficult map skill to learn. Much confusion results when students are
told that latitude lines go east-west and longitude lines go north-south. Avoid this description. Before they
can find the latitude or longitude of a place, they must be able to identify the Equator and the Prime
Meridian on any map. Latitude is position north or south of the Equator. Latitude lines are parallel to the
Equator. The numeric values of latitudes are obtained from the sides of the map and are given an N if they
are north of the Equator and an S if they are south of the Equator. Longitude is position east or west of the
Prime Meridian. Longitude lines converge at the poles. Longitude values are obtained from the top or
bottom of the map and are given an E if they are east of the Prime Meridian and a W is they are west of the
Prime Meridian up to a value of 180. If students are taught latitude and longitude as stated in sentence #2,
they will have difficulty figuring out whether to use N, S, E, or W and will likely get it wrong. It is not a
latitude or a longitude unless it has the appropriate letter. It might be helpful to treat latitude and longitude
separately until students can get the difference.
In the map below, the earth is divided into four quadrants by the Prime Meridian (which passes through
Greenwich, England and is green here) and the Equator (red). The lines are 15° apart, which is standard
on most maps. See if you can find the latitude and longitude of the four points identified as A, B, C, and D
and then check your work at the end of this SOL bullet.
C
A
0
B
D
0
Topographic profiles can be drawn exactly knowing the scale and the contour interval of a topographic
map; however, this requires fine motor skills and is not necessary at the high school level. Instead,
students may be given a map and told to draw a rough approximation of a side view of the land between
two points. They should divide the cross section up into shorter segments and determine whether the land
falls or rises in a segment and whether the land is steep or flat in each segment. Use the clues given in the
section on topography above.
Answers to the latitude and longitude:
A 15 N and 120 W
B 30 S and 105 E
C 45 N and 150 E
D 45 S and 90 W
After reviewing material in your textbook and exploring the websites above, go to the file labeled ES.3
Review Responses and open it in Word. Type your answers below each question and make them a
distinctive readable color or font. E-mail this file as an attachment word document to the address provided
in the introduction. Please make your answers succinct.