How to read Topographic Map by benbenzhou


									How to read a Topographic
What is the difference between topographic maps
                 and other maps?

Topographic map     - Represent cultural and
                      natural features
Chorographic maps   - Cover large regions
Planimetric maps    - Do not show elevations
Thematic maps       - Focus on specific topics
Photographic maps   - Use of photo as map
Digital Maps        - Digitized map data
               Planimetric Maps

Present the horizontal position of selected features but
                   do not show relief

Examples of planimetric maps are base, cadastral, line-
               route, and outline maps.
                 Topographic Maps

Portray the shape and elevation of the terrain.

for various purposes:
- selecting sites
- planning highways
- routing utility lines
- electing dam sites
                       Topographic Maps

                            can be classified by scale

Large-scale maps (1:24,000-scale maps)
   useful for highly developed areas or rural areas where detailed
        information is needed for engineering, planning or similar purposes.

Intermediate-scale maps (from 1: 50,000 to 1:100,000)
         cover larger areas and are especially suited for land management
                                 and planning.

Small-scale maps (1:250,000, 1:500,000, and 1:1,000,000)
       useful for comprehensive views of extensive projects or for regional
                             Thematic Maps
Thematic maps are also called geographic, special-purpose, or distribution
They emphasize a single topic, such as geology, climatology, or crop
   distribution, and the entire map is devoted to presenting this distribution.

Geographers use thematic maps to
show the distribution of subjects
such as population,

languages, crop production, soil,
climate, vegetation, land use, and
                                  Digital Maps

Data-processing systems have made it possible to store digitized map data either in
graphic form as a digital map or in numerical form as a body of data.

The location and elevation
of all bridges in a given
area can be obtained from
the    data     bank      and
automatically plotted on a
map or listed in terms of
horizontal     and     vertical
They are an alternative to the other maps, they show nonselective
details requiring photo interpretation by the user.
Some people like the term Topographic Maps

while others prefer       Topographical Maps

Both terms are correct, and mean the same thing.
              Definition of a map

 A graphic representation of a portion of the
earth's surface drawn to a scale. It uses colors,
symbols, and names to represent features found
on the ground .
       Definition of a topographic map

 A topographic map is a detailed and accurate
graphic representation of cultural and natural
features on the ground

                       The Canadian Centre for
                       Topographic Information
        Definition of a topographic map

is characterized by large-scale detail and
quantitative representation of relief, usually using
contour lines in modern mapping, but historically
using a variety of methods.
       What is the difference between
     topographic maps and other maps?

A unique characteristic that distinguishes
topographical maps from other kinds of maps is
the fact that they show the topography or shape
of the land in addition to other features such as
roads, rivers, lakes, etc.
        What is the difference between
      topographic maps and other maps?

Contours are imaginary lines that join points of equal
elevation on the surface of the land above or below a
reference surface.

Contours make it possible to measure the height of
mountains, depths of the ocean bottom, and
steepness of slopes.
           Why topographic maps?

Because topographical maps show the shape of
the land, it is the most suitable map for most
outdoor activities that take place in areas that are
not heavily populated.
          Why topographic maps?

A topographic map shows more than
contours. The map includes symbols that
represent such features as streets,
buildings, streams, and vegetation.
           Why topographic maps?

Topographic maps represent a incredible
resource for educators and learners.
They can be used in a variety of ways in the
science, geography, and history curriculum, from
elementary to university level.
                   Brief history
In the 1670s Giovanni Domenico Cassini
persuaded to make a detailed map of France.

After Cassini's death, his children and
grandchildren continued to labor on the project.

The final result, called the Carte de Cassini, was
published in 1793 and was the first accurate
topographic map of an entire country.
      Topographic maps in Sri Lanka

1: 250,000
Sri Lanka One Inch Map (One mile to an inch)

72 map sheets cover the whole Island
Relief Contours at 100ft. Intervals
First Edition Completed in 1924
Last revision in 1985
            Sri Lanka 1: 50,000

Scale 1:50,000
92 map sheets to cover the whole Island
Relief -Contours at 20m /100ft intervals
First Edition started in 1985
Revised Edition started in 1999
Sri Lanka   1: 50,000
           Sri Lanka 1: 10,000

1834 map sheets cover the whole Island
Relief - Contours at 2m /5m /10m intervals
           Sri Lanka 1: 250,000

4 map sheets to cover the whole Island
First edition 1992
Data source - Complied from 1:50,000 maps
The USGS published approximately 57,000
different topographic maps covering the
          Reading topographic maps

Features are shown as points, lines, areas and
names depending on their size and extent.

Interpreting the colored points, lines and areas, is
the first step in reading topographic maps.
     Reading Topographic Maps - Areas

The first features usually noticed on a
topographic map are the area features, such as
vegetation (green), water (blue), and densely
built-up areas (gray or red).
       Reading Topographic Maps - Lines

Many features are shown by lines that may be straight,
curved, solid, dashed, dotted, or in any combination.

The colors of the lines usually indicate classes of
information: topographic contours (brown); lakes,
streams, irrigation waterways, and other hydrographic
features (blue); land grids and important roads (red); and
other roads (yellow) , railroads, boundaries, and other
cultural features (black).
     Reading Topographic Maps - Points

Various point symbols are used to depict features
such as buildings, springs, water tanks, mines,
survey control points, and wells.
    Reading Topographic Maps - Names

Names of places and features are shown in a
color corresponding to the type of feature.
Many features are identified by labels.
    Reading Topographic Maps - Contours

Contours are shown in brown by lines of different
widths. Each contour is a line of equal elevation;
therefore, contours never cross.
They show the simplified shape of the terrain.
Index contours are wider. Elevation values are printed in
several places along these lines.
Intermediate and supplementary contours are narrower
and found between the index contours help to show
more details of the land surface shape.
 Reading Topographic Maps Contour lines

Contours that are very close together represent steep
Widely spaced contours or an absence of contours
means that the ground slope is relatively level.
The elevation difference between two contour lines
called the contour interval.
           Relief Contour lines
number written on line
between Index lines
added to flat areas to
show measurements
            Bathymetric contours

Bathymetric contour

They are shown in blue or black, depending on
their location.
They show the shape and slope of the ocean
bottom surface.
The bathymetric contour interval may vary on
each map and is explained in the map margin.
     Marginal information and symbols

A map could be compared to any equipment.

Before it is placed into operation, the user must
read the instructions.

The marginal information and symbols, where
useful information telling about the map, are
useful for this requirement.
                   Sheet Name

It is found in bold print at the center of the top.

A map is generally named for the main
settlement contained within the area covered by
the sheet.

Sometimes, the largest natural feature located
within the area is also used.
                 Sheet Number

The sheet number is found in bold print in both
the upper right and lower left areas of the
margin, and in the center box of the adjoining
sheets diagram (Location), which is found in the
lower right margin.

It is used as a reference number to link specific
maps to overlays, operations orders, and plans.
                  Series Name

The map series name is found in the same bold
print as the sheet number in the upper left corner
of the margin.
           Representative Fraction
The scale is found both in the upper left margin
after the series name, and in the left of lower
The scale note is a representative fraction that
gives the ratio of a map distance to the
corresponding distance on the earth's surface.
The scale 1:50,000 indicates that one unit of
measure on the map equals 50,000 units of the
same measure on the ground.
                  Linear Scales

These are located in the left of the lower margin.
They are rulers used to convert map distance to
ground distance.
Maps have two bar scales, in km and miles.
Care should be exercised when using the scales,
especially in the selection of the unit of measure
that is needed.
                 Series Number

The series number is found in the lower left

For example: A.B.M.P.
               Edition Number

The edition number is found in bold print in the
lower left area of the bottom margin.
Editions are numbered consecutively; therefore,
if you have more than one edition, the highest
numbered sheet is the most recent.
The map edition date is found in the lower right
margin of the map. This date is important when
determining how accurately the map data might
be expected to match what you will encounter on
the ground.
            Administrative Index

The index to boundaries diagram appears in the
lower or right margin of all sheets.
This diagram, which is a miniature of the map,
shows the boundaries that occur within the map
    Adjoining Sheets Diagram - Location

Maps contain a diagram called Location that
illustrates the adjoining sheets.
It consists of nine rectangles representing eight
adjoining sheets necessary to surround the
rectangle that represents the sheet under
The diagram usually contains nine rectangles.
All represented sheets are identified by their
sheet numbers and sheet names.
                Elevation Guide

This is normally found in the lower left margin.
The elevation guide provides the map reader with
information on datum, and elevation

Datum for all level is the Mean Sea Level (MSL)
         What Is Mean Sea Level (MSL)?

The height (H) above an imaginary surface called the geoid,
is determined by the earth's gravity and approximated by
MSL is usually described as a tidal datum that is the
arithmetic mean of water elevations observed over a 19-
year cycle.
MSL is defined as the zero elevation for a local area.
However, MSL differs from one country to another

This is located in the lower margin of maps and
indicates the angular relationships of true north,
grid north, and magnetic north.

There is a note indicating the conversion of
azimuths from grid to magnetic and from
magnetic to grid next to the declination diagram.

     MN      TN
                     True North

True North (Geographical North) is a line from any
point on the earth's surface to the north pole(900 N)
All longitudes are true north lines.
True north is usually represented by TN.
                Magnetic North

Magnetic North is the direction to the north
magnetic pole, as indicated by the north-seeking
needle of a magnetic instrument.

Approximately 11° difference exists between True
North and Magnetic North. Currently located in
Canada about 1,300 km from True North.
                  Grid North

Grid North is established by using the vertical
grid lines on the map.

Grid north may be symbolized by the letters
GN or the letter. Grid North is not equal to
True North.
          North- Declination Diagram

Grid-Magnetic Angle.
The GM angle value is the angular size that exists
between grid north and magnetic north.
It is an arc, indicated by a dashed line, that
connects the grid-north and magnetic-north
The GM angle is important to the map reader
because azimuths translated between map and
ground will be in error by the size of the
declination angle if not adjusted for it.
          North- Declination Diagram

Grid Convergence.

An arc indicated by a dashed line connects the
prongs for true north and grid north. The value of
the angle for the center of the sheet is given to the
nearest full minute with its equivalent to the
nearest mil.
These data are shown in the form of a grid-
convergence note.
             Contour Interval Note

This note is found in the left of the lower margin
below the bar scales. It states the vertical
distance between adjacent contour lines of the
When supplementary contours are used, the
interval is indicated.
In recent edition maps, the contour interval is
given in meters (20 meters) instead of feet.
                    Grid Note

This note is located below the Location grid of
the lower margin.
It gives information pertaining to the grid system
used and the interval between grid lines.
                 Projection Note

The projection is the framework of the map.
This framework is of the conformal type;
       (a) small areas of the surface of the earth
retain        their true shapes on the projection;
       (b) measured angles closely approximate true
       (c) scale factor is the same in all directions
from a point.
The projection note is located below the bar scale.
               Projection Note
    Between 80° south and 84° north, maps at
    scales larger than 1:500,000.
    Between 80° south and 84° north, maps at
    1:1,000,000 scale and smaller
    Maps of the polar regions (south of 80°
    south and north of 84° north) at 1:1,000,000
    and larger scales
Cylindrical Projection
 Mercator Projection

Cylinder tangent ^iam¾Ylh&
      at the Equator
   Transverse Mercator Projection

Cylinder tangent ^iam¾Ylh&   Conformal
    to Central meridian      for shape
Oblique Mercator Projection
Transverse Mercator Projection
If you see the features on the map and you will
   understand how a topographic map works.
            The contour lines are very
            close together, indicating
            an extremely steep slope
            that rises from 4500 feet
            to 5100 feet and a circular

            The open center circle
            inside the 5100 contour
            line indicates that the top
            of the mountain is a flat

A   B   C                    D
              Types of slope -Gentle
Contour lines showing a uniform, gentle slope will be
evenly spaced and wide apart . Considering relief
only, a uniform, gentle slope allows the defender to
use grazing fire. The attacking force has to climb a
slight incline.
              Types of slope -Steep
Contour lines showing a uniform, steep slope on a
map will be evenly spaced, but close together.
Remember, the closer the contour lines, the steeper
the slope.
             Types of slope -Concave
Contour lines showing a concave slope on a map will
be closely spaced at the top of the terrain feature and
widely spaced at the bottom.
           Types of slope -Convex
Contour lines showing a convex slope on a
map will be widely spaced at the top and
closely spaced at the bottom.
              Terrain features - Hill
A hill is an area of high ground. From a hilltop,
the ground slopes down in all directions. A hill
is shown on a map by contour lines forming
concentric circles. The inside of the smallest
closed circle is the hilltop
           Terrain features - Saddle
A saddle is a dip or low point between two
areas of higher ground. A saddle is not
necessarily the lower ground between two
hilltops; it may be simply a dip or break along a
level ridge crest.
           Terrain features - Valley
A valley is a stretched-out groove in the land,
formed by rivers. A valley begins with high
ground on three sides, and usually has a
course of running water through it. Contour
lines forming a valley are either U-shaped or V-
            Terrain features - Ridge
A ridge is a sloping line of high ground. Contour
lines forming a ridge tend to be U-shaped or V-
shaped. The closed end of the contour line
points away from high ground .
         Terrain features - Depression
A depression is a low point in the ground or a
sinkhole. It could be described as an area of
low ground surrounded by higher ground in all
directions. Usually only depressions that are
equal to or greater than the contour interval will
be shown.
            Terrain features - Draw
A draw is a less developed stream course than
a valley. In a draw, there is essentially no level
ground and, therefore, little or no maneuver
room within its confines. A draw could be
considered as the initial formation of a valley.
            Terrain features - Spur
A spur is a short, continuous sloping line of
higher ground, normally jutting out from the
side of a ridge. A spur is often formed by two
rough parallel streams, which cut draws down
the side of a ridge.
              Terrain features - Cliff
A cliff is a vertical or near vertical feature; it is
an abrupt change of the land. When a slope is
so steep that the contour lines converge into
one "carrying" contour of contours, this last
contour line has tick marks pointing toward low
             Terrain features - Cut
A cut is a man-made feature resulting from
cutting through raised ground, usually to form a
level bed for a road or railroad track. Cuts are
shown on a map when they are at least 10 feet
high, and they are drawn with a contour line
along the cut line.
              Terrain features - Fill
A fill is a man-made feature resulting from filling
a low area, usually to form a level bed for a
road or railroad track. Fills are shown on a map
when they are at least 10 feet high, and they
are drawn with a contour line along the fill line.
Using contour lines
A. There are no contour lines around this
location so it is relatively flat here.

B is at about 11,760 feet

X and Y, at about 10,800 feet.
A   3      - Gradual, consistent slope
B   5/ 8   - Draw or valley with stream
C   13/4   - Cliff face
D   12     - Hill with ridge
E   9      - Spurs on a mountainside
F   10     - Depression
G   4/13   - Cliff face
H   7      - Steeper slope high, gradual low
I   1      - Consistent slope
J   2      - Gradual slope high, steeper low
K   11     - A saddle between two hills
L   8/5    - Draw or valley with stream
M   6      - Simple round hill
 Analyzing Physical Features on Topographic

How are the physical features identifiable on
topographic maps?

How do physical features affect population ?

What forces are most active on the landscape in this
area? Landslides? Floods? Erosion?

Can you plan a road from point A to point B through a
mountainous region.
 Analyzing Cultural Features on Topographic
What are the major economic activities of the area shown
on the selected topographic map?
How are these activities reflected in the cultural, or
human-built, features on the map?
Is this a fast or slow-growing, or declining, area, and why?
What forces act to limit or promote growth?
Why are certain land uses concentrated in certain areas?
                  Site vs Situation

Site refers to the physical attributes of a location.

 Situation refers to the advantages and
disadvantages of one location over another location,
considering urbanization, transportation, and so on.

How to use a topographic map for site vs situation
comparing two different locations.

Discuss selecting a land for a planned city.
               Creating Aspect Maps
Aspect refers to the direction (north, east, south, west)
that the slope faces.

Make an aspect map by examining contour lines.

Compare the vegetation on north-facing versus south-
facing slopes.

Compare health of the people living on slopes east-facing
versus west-facing.

Discuss earth-sun relationships.
Analysis of Humans settlements and Hydrography

How do rivers encourage (e.g. transport) and discourage
(e.g. flooding) settlements?

Why does place near a large river attract a large city, while
the other place is sparsely populated?

This may occur if one place was higher and flood-free, and
the other was flood-prone.

What is the elevation of both places?
 Location of the city of Durham, UK

          Topographic Map Skills

When reading a topographic map, you need
to visualize in your mind's eye a 3-
dimensional view of what the symbols and
contour lines are representing.
Using a Map and Compass

If you understand how to read a compass and
how to read a map, then its about time you
learned to use both map and compass together.

Separately, a good map or compass can be very
useful, but limited. Together, they can lead you
around the world but you need to know how to
use them properly.
How a Compass Works

There is a huge magnetic field around the earth. It
is huge, but it is not very strong. The magnetized
needle in a compass is aligned with this magnetic
field. As the image below shows, the composition
of the earth acts as a huge bar magnet sitting
upside down in the middle of the planet. Since its
South end is at the north pole and its North end is
at the south pole, the North end of a compass
needle is pulled north.
Map Symbols
Since a map is a reduced representation of the real
world, map symbols are used to represent real objects.
Without symbols, we wouldn't have maps.
Both shapes and colors can be used for symbols on
maps. A small circle may mean a point of interest, with a
brown circle meaning recreation, red circle meaning
services, and green circle meaning rest stop. Colors may
cover larger areas of a map, such as green representing
forested land and blue representing waterways.
To ensure that a person can correctly read a map, a Map
Legend is a key to all the symbols used on a map. It is like
a dictionary so you can understand the meaning of what
the map represents.

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