Topographic Surveys
Topographic Surveys
Topographic maps
Topographic maps
• Vertical
Vertical data (elevation, height) are the data (elevation height) are the
distinguishing characteristic of topographic maps
• Topographic maps show the configuration or shape and roughness of the ground; this
shape and roughness of the ground; this roughness is commonly referred to as relief
• Throughout time, depiction of the relief of a Th
h
i
d i i
f h
li f f
parcel of land has changed
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Paul C. Ampong
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Topographic surveys
Topographic surveys
• Topographic surveys involve all procedures, opog ap c su eys o e a p ocedu es,
equipment and methods necessary to capture both horizontal and vertical data of points on the ground so strategically chosen to depict the d
ll h
d
h
terrain
• Modern topographic maps represent points that M d
t
hi
t i t th t
have identical elevations with lines called “contours”
contours
• The elevation on these lines are based on known or assumed datum
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Paul C. Ampong
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Sugar loaves
Sugar loaves
• These
These are idealized depiction from a side or are idealized depiction from a side or
oblique view; the only form of topography on early maps (pre‐1700)
early maps (pre
1700) due to lack of detailed due to lack of detailed
surveying; gives location of mountains/hills but not precise size
but not precise size.
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Paul C. Ampong
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Sugar loaves
Sugar loaves
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Sugar loaves
Sugar loaves
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Hachures
• Hachuring use lines of varying width and length g
y g
g
to depict slope steepness, drawn in direction of the slope. Initially unsurveyed and little better than sugar loafs the first form known giving
than sugar loafs, the first form known giving general location of mountain ranges are referred to as 'hairy caterpillars‘
• In modern maps, hachures are not often used except when the scale of the map is too small to permit contouring
permit contouring
• If properly drawn, they convey a good concept of the terrain, but their value is largely pictorial
Topographic Surveys; Prepared by Andre‐
Paul C. Ampong
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Hachures
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Paul C. Ampong
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Hachures
• They were systematized in 1799 by Major Lehmann, an Austrian military officer, where line width became directly proportional to steepness. It hence became q
quite commensurable, but not very imageable: blank y
g
on top and in valleys, and shortly after a North‐West light source was introduced to enhance imageability. This was the main type of relief depiction through the yp
p
g
19th century
• After accurately surveyed heights became available through the 20th century hachures gave way to through the 20th century, hachures
gave way to
contours, but they are still used for very steep slopes such as cliffs, quarries and railway cuts, where contour lines would merge
lines would merge.
Topographic Surveys; Prepared by Andre‐
Paul C. Ampong
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Hachures
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Paul C. Ampong
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Hachures
• Disadvantages:
Disadvantages: –
–
–
–
–
Lack of absolute information
Difficulty in distinguishing the direction of the slope
Difficulty in distinguishing the direction of the slope Time‐consuming to produce
Obscures other information
Obscures other information
Not very effective except in mountainous terrain
• Advantage
– They may show minor but important details otherwise lost on a contour map within the contour intervals
Topographic Surveys; Prepared by Andre‐
Paul C. Ampong
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Hachures
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Paul C. Ampong
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Contours
• Contours came
Co tou s ca e initially from the need to know t a y o t e eed to o
exact depths in water, and were generated from a series of depths or soundings. The first contours in the late 1900’s were on navigation charts as h l
’
h
'isobaths' (since hachuring was not suitable for an unseen landscape)
unseen landscape).
• A contour is essentially an isarithm or an isopleth: a line drawn on a map through all points
isopleth: a line drawn on a map through all points having the same numerical value, as of a population figure or geographic measurement
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Paul C. Ampong
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Contours
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Contours Contours
• Characteristics: – Contour interval (the distance between contour lines) is determined by terrain and map scale – Index contours are symbolized as wider lines and I d
b li d
id li
d
usually every 5th contour
– Form lines are approximate elevations (not o
es a e app o a e e e a o s ( o
accurately surveyed)
– Depression contours (enclosing lower land) are drawn with small tick marks inside
drawn with small tick marks inside. Topographic Surveys; Prepared by Andre‐
Paul C. Ampong
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Contours
• Basic rules
–
–
–
–
–
–
–
–
A contour line must never split or divide.
A contour line must never simply end except at the edge of the map. A contour line must represent one and only one elevation
A contour line must represent one and only one elevation. A contour line may never intersect other contour lines. Overhanging cliffs are the only exception. C
Contour lines from a V‐pattern crossing stream always points li
f
i
l
i
upstream. Closely spaced contour lines represent a steep slope, widely spaced li
lines indicate a gentle slope. i di
l l
Concentric circles of contour lines indicate a hilltop or mountain peak. Concentric circles of hachured contour lines indicate a closed depression.
Topographic Surveys; Prepared by Andre‐
Paul C. Ampong
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Contours
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Contours
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Contours
• Advantages g
– it is the most commensurable (quantitative) method – it is the origin for many (most?) newer depiction techniques and it is now familiar to many users
techniques, and it is now familiar to many users. • Disadvantages – it is an abstract method (there are no counterpart to (
p
lines on ground); poorly suited to small scales – less imageable but depending on: contour interval, map scale, landscape type, and users' experience. map scale, landscape type, and users
experience.
These disadvantages were recognized early on and led to other methods being developed . Topographic Surveys; Prepared by Andre‐
Paul C. Ampong
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Hypsometric tints
Hypsometric tints
• The
The addition of colour
addition of colour to elevation levels, first to elevation levels first
tried as early as 1830. Color schemes require graduation logical sequence realistic colors
graduation, logical sequence, realistic colors, with the darkest still able to bear readable text. text
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Paul C. Ampong
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Hypsometric tints
Hypsometric tints
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Paul C. Ampong
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Hypsometric tints
Hypsometric tints
• Advantages g
– adds imageability, mostly at small scale; easily applied and understood • Disadvantages Disadvantages
– exaggerated terrace effect, no new real 'information' is added, – differential contrast between tints and other elements, dubious color associations, (green with forest, etc.) (g
)
– which colour scheme?.. chroma of the same hue, or spectrum range ‐ green ‐> yellow ‐> red Topographic Surveys; Prepared by Andre‐
Paul C. Ampong
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Hypsometric tints
Hypsometric tints
Topographic Surveys; Prepared by Andre‐
Paul C. Ampong
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Hypsometric tints
Hypsometric tints
Topographic Surveys; Prepared by Andre‐
Paul C. Ampong
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Shaded relief (hill shading)
Shaded relief (hill shading)
• This
This involves the addition of shadows to give involves the addition of shadows to give
the illusion of depth, assuming a theoretical NorthWest light source (at 45 degrees light source (at 45 degrees
elevation). It was introduced in the 1900’s but became more widespread after 1960 with
became more widespread after 1960, with improved printing technology and user needs. It has become much more common with
It has become much more common with automation.
Topographic Surveys; Prepared by Andre‐
Paul C. Ampong
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Shaded relief (hill shading)
Shaded relief (hill shading)
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Paul C. Ampong
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Shaded relief (hill shading)
Shaded relief (hill shading)
• Advantages g
– highly imageable, continuous in appearance (as in reality), can show greater detail and character of landscape
suitable over a variety of scales and as a general background for a variety of map types • Disadvantages – Manually
Manually required artistic creation with pencil or air required artistic creation with pencil or air
brush; It was costly and often poorly rendered, when done manually. It creates a variable background with some slopes very dark
p
y
Topographic Surveys; Prepared by Andre‐
Paul C. Ampong
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Tanaka (relief) contours
Tanaka (relief) contours
• This technique of applying a northwest light s tec que o app y g a o t est g t
source to a contoured landscape was first tried in 1850 but printing methods then could not handle gray backgrounds (to be able to highlight b k
d ( b bl
h hl h
illuminated lines). • It was pioneered from the 1950s by Kitiro Tanaka who produced some exquisite examples using the
who produced some exquisite examples using the theory of application of shading principles to contouring.
Topographic Surveys; Prepared by Andre‐
Paul C. Ampong
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Tanaka (relief) contours
Tanaka (relief) contours
Topographic Surveys; Prepared by Andre‐
Paul C. Ampong
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Block (perspective) diagrams
Block (perspective) diagrams
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Paul C. Ampong
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Block (perspective) diagrams
Block (perspective) diagrams
• Advantage:
– the most imageable portrayal of landscape (3D), often used for ski hills and panoramas
often used for ski hills and panoramas
• Disadvantages
Di d t
– the most time‐consuming to produce with no consistent linear scale, (before computers)
i t t li
l (b f
t )
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Paul C. Ampong
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